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    Civil Engineering

    Encyclopedia Arctica 2a: Permafrost-Engineering




    001      |      Vol_IIA-0284                                                                                                                  

    Cold Weather Operations

    EA-I. (Palmer W. Roberts)

    COLD WEATHER OPERATIONS

            Increased activity in the arctic region has focused attention on the

    engineering problems encountered. In considering cold weather operations, it

    would be hard to find a field of human knowledge in which the past reveals so many

    practical guideposts for the present and upon which plans can be made for the

    future.

            Operations in the Arctic and Subarctic do not vary greatly from those

    in the North Temperate zone. There are, however, certain variations in field

    practices, construction methods, and engineering design necessary to meet the

    requirements imposed by climate, terrain, and other local factors. In approach–

    ing such problems, the peculiarities of the area must be accepted and the usual

    design, materials, and construction techniques modified accordingly. The effi–

    cient and effective use of all resources and conditions in the Arctic must

    greatly influence the application of all engineering principles. It is necessary

    to work with nature and not against her in the Arctic.

            In the space assigned the subject of engineering in the Encyclopedia

    Arctica , it would not be possible to cover the many subjects in the fields of

    engineering for each country or area where special problems may be encountered.

    It has, therefore, been necessary for the authors to treat many of the subjects

    only in specific areas. In the main, the articles are concerned with operations

    in the northern regions of the North American continent. However, the princi–

    ples and techniques discussed may serve as a guide for other areas, after

    002      |      Vol_IIA-0285                                                                                                                  
    EA-I. Roberts: Cold Weather Operations

    analyzing local conditions.

            In planning for operations in the Arctic, logistics, or providing the

    means for supporting and accomplishing the task, may often prove to be the

    limiting factor. The absence of rail and road nets, the difficulty of move–

    ment overland both in winter and summer, the lack of ice-free ports in the

    winter and the short period in the summer when vessels may operate, and the

    limitations imposed on flying by poor visibility near bodies of water during

    certain periods of the year, are a few of the many factors relating to the

    area which must be considered. The maintenance and operation of equipment

    under the variety of conditions imposed by extreme weather and terrain, and

    the providing of at least the minimum of bodily comfort in the manner of

    clothing and shelter for personnel, as well as proper food and adequate train–

    ing, are problems that must be solved for each operation.

            A thorough knowledge of the physical character of the Arctic during

    all seasons of the year is also essential to the success of any operation

    (see “Work Feasibility”). Surface and subsurface conditions vary greatly

    with the season in the Arctic. Vast quantities of ice form in the winter

    and much of it remains in the seas during the summer. The presence of ice as

    a rock, or as a rock constituent of frozen ground, presents a major subsurface

    problem for study (see “Permafrost”).

           

    Palmer W. Roberts



    Unpaginated      |      Vol_IIA-0286                                                                                                                  

    Work Feasibility

    EA-I. Roberts; Work Feasibility

           

    LIST OF FIGURES

    Page
    Fig. 1. Work feasibility chart 5-a



    001      |      Vol_IIA-0287                                                                                                                  
    EA-I. (Palmer W. Roberts)

           

    WORK FEASIBILITY

            In the northern regions and seasonal variations in climate and terrain

    are extreme, yet the cold does not establish a barrier for human activity.

    Climatic conditions do become a major factor when dealing with problems in

    design and construction engineering. Climate has been said to be the annual

    or long-term result of weather, and weather the result of nature’s effort to

    balance the heat equation of the hemisphere. To provide a general background

    of weather as it relates to engineering in the northern regions, major climate

    factors - temperature, wind, precipitation, visibility, and light - are briefly

    discussed herein.

            Temperature . In the northern areas great temperature differences prevail.

    The coldest temperature ever recorded in the northern regions was at Verkhoiansk,

    Siberia, where −93.5°F. was reported. The lowest temperature in North America

    ever recorded was −81°F. at Snag. Yukon Territory. Fort Yukon, just north of

    the Arctic Circle in Alaska, has a U.S. Weather Bureau record of 100°F. in the

    shade and considerably higher extremes have been reported at several places in

    the North American and European Subarctic. Thus, it is apparent that the extreme

    temperature range (Fahrenheit) for the Arctic can be placed at approximately

    195 degrees; in Alaska the spread is approximately 185 degrees.

            Wind . The frequency and velocity of high winds in the Arctic is are not as

    002      |      Vol_IIA-0288                                                                                                                  
    EA-I. Roberts: Work Feasibility

    great as in the other zones. Stronger winds, and more frequent strong winds,

    are experienced in the winter along the coast than are found in the interior

    at that time; in summer the differences are not so great. The frequency of

    strong winds in the North American Arctic resembles that of Siberia. At

    Point Barrow, Alaska, the maximum velocity so far recorded (up to 1950) for

    the winter months is something over 100 m.p.h. but for the summer only 41 m.p.h.,

    with the average annual mean at 12 m.p.h.

            Precipitation is light in the Arctic. The annual total of melted snow

    and rain may not exceed 10 inches per year in most of the Alaska and Canadian

    Arctic, and is probably even less in the Soviet Arctic. It is difficult to

    obtain accurate measurements of snow, due to the light and fluffy nature of

    the crystals and their tendency to migrate under less than average wind velocity.

    Snow may fall in any month. In the winter the precipitation is mainly in the

    form of snow and is generally very light, except that fairly heavy snowfall occurs

    in certain foothill and mountain areas. At Point Barrow, where accurate

    aerological measurements are maintained throughout the year, the maximum snowfall

    occurs in October, eight inches having been recorded during this month. Very

    light rains are experienced throughout the Arctic in the summer, with the

    maximum occurring during July and August. Thunder is rare.

            Visibility . Fog and poor visibility provide difficulties for arctic

    operations and ofttimes limit e a viation and ship operations along the coast.

    Fogs are usually most dense at the borders of the ice. The land senses of

    the Arctic are warmer than the sea in the summer and colder in the winter.

    Thus winds passing from either belt across the other are liable to produce fog.

    The most severe fog conditions are experienced in spring and in the fall

    when a visibility of a mile or less occurs more than 20% of the time. Cloudless

    003      |      Vol_IIA-0289                                                                                                                  
    EA-I. Roberts: Work Feasibility

    days (0 to 0.2 coverage) are not common along the arctic coasts, but do occur

    during December and January, the clearest months.

            Light is a rather peculiar problem is polar regions; it is received from

    the direct and refracted rays of the sun, the moon, the stars, the planets,

    and from the aurora borealis. The sun remains above the horizon, because of

    refraction, for something over six months at the Pole, nearly four and one-half

    months at 80° N., and for over eighty days at Point Barrow, 71°23′ N. It is

    never pitch dark at night in the North and there is more effective light in

    these areas than in the tropics or temperate zones. This is because of

    several factors, namely:

    1. Cold, clear, dust-free air transmits light more readily.

    2. During the period of no direct sunlight, the snow and ice cover

      reflects and magnifies all light that it receives from the various light sources.

    3. When the ground is not covered with snow, there is perpetual direct

      and reflected sunlight.

    4. The starts, moon, and aurora succeed in delivering a high percentage

      of their produced light to the earth during the winter.


            Maximum arctic darkness occurs in winter when the sky is densely overcast,

    when there is no moon or twilight, and when there is no aurora behind the

    clouds. However, even under such maximum darkness conditions, a man clad in

    dark clothing can be seen a distance of about one hundred yards against a

    snow or ice background. In winter the aurora borealis display is frequent;

    in the summer it can be seldom be seen because of continuous light. They Auroras are of

    varied description and undergo rapid changes in form. Some of these forms may

    be described as arcs, rays, streaks or lances, bands, curtains or draperies,

    004      |      Vol_IIA-0290                                                                                                                  
    EA-I. Roberts: Work Feasibility

    coronas, diffused light, crowns, and cloud-shaped. They c v ary greatly in

    color (see “The Aurora Borealis”).

            The effect of the extreme variations in climate on engineering operations

    can best be realized by comparing the physical character of the arctic surface

    and subsurface during the extreme periods of winter and summer. Permanently

    frozen ground, called permafrost, is a widespread phenomenon, common through–

    out North America and northern Asia; about one-fifth of the land area of the

    world is underlain by permafrost. Temperature within permafrost varies during

    the year generally from 16° f t o 30°F. In the upper layer of the ground, which

    is not permanently frozen, the effects of seasonal thawing are usually more

    severe than in areas not underlain by permanently frozen material. It has

    been determined that stresses developed in freezing ground may exceed 28,000

    pounds per square inch. When ground conditions established by nature are

    disturbed during construction, the thermal equilibrium must be restored as

    quickly as possible. Groundwater may exist in frozen or thawed ground and,

    as migrating water transmits heat, many of the problems of freezing and thawing

    are related to it. In winter, drifting snow creates many problems and, there–

    fore, is always considered when selecting sites for building or routes for

    freighting operations. In the summer, snow remains on the ground in lowland

    areas for short periods only.

            Thickness of the ice on the rivers, on the lakes, and on the Arctic Sea,

    is important in connection with transportation. In northern Alaska, ice begins

    to form on fresh-water lakes early in September and on salt water usually the

    latter part of the same month. Maximum thickness of ice is reached in early

    May on both fresh- and salt-water bodies.



    005      |      Vol_IIA-0291                                                                                                                  
    EA-I. Roberts: Work Feasibility

            From even this brief description it can be deduced that the weather during

    the major part of the year is such that detailed analysis of climatic factors

    will be required before units can be committed to arctic field operations. The

    principal factors to consider are as outlined: light, temperature, wind (the

    combined wind-chill factor), precipitation (snow and rain), ceiling, visibility,

    and the thickness of ice and other factors of sea condition. A comparison of

    the above and of the work or mission to be accomplished is necessary. As an

    aid in making such an evaluation, a chart of the factors may be of assistance

    (see Fig. 1). On this chart are shown the factors of climate and the work or

    mission to be accomplished, such as transportation, construction, and water

    supply. Examining the month of February, the following factors are noted.

            Daylight: 3 hours increasing to 9 hours with an additional 1-1/2 hours

    of twilight per day.

            Ceiling: 1,000 feet or lower, 19% of the month.

            Visibility: one mile or less, 14% of the month.

            Temperature: absolute maximum, 35°F; mean maximum −15°; mean tempera–

    ture, −20°; mean minimum −25°; absolute minimum −56°.

            Wind: maximum recorded, 71 miles per hour; average, 10 miles per hour;

    direction SW. 43%, NE. 15%.

            Wind chill: varying from B, fair for traveling, to E, extreme limit

    for operations.

            Precipitation: 4 inches of snow; trace of rain.

            New ice thickness: ocean, 40 inches increase to 50; lakes and rivers,

    48 inches increase to 54.

            Reviewing these it is noted that over-ice freighting with tractors and

    sleds can be conducted. Ground surface will support wheeled vehicles, tractors,

    005a      |      Vol_IIA-0292                                                                                                                  

    Fig. 1. Work Feasibility Chart.



    006      |      Vol_IIA-0293                                                                                                                  
    EA-I. Roberts: Work Feasibility

    and sleds . can be conducted. Ground surface will support wheeled vehicles,

    tractors, and sledo.
    Planes can operate on skis throughout the area and on

    wheels from prepared strips. However, the number of flying hours per day is

    limited by daylight (moonlight can be used for supplementary purposes for

    several days either side of the full, if the sky is clear). Shallow lakes

    and rivers will be frozen but water can be taken from deeper lakes or obtained

    from melting ice or snow. Due to poor visibility and cold, surveying is not

    recommended. Earth work is not possible at this season but foundation work

    can be accomplished by the use of explosives or by thawing methods. For

    outside construction work, flood lighting will be required. The month of

    February could be utilized to repair equipment in shops and accomplish inside

    construction. All equipment to be used out of doors will required complete

    winterization, arctic lubricants and fuels, and heated inside storage.

    Personnel will require adequate protection, proper clothing, and indoctrination.

            This same procedure, analyzing the climatic and operating factors, can

    be followed for each month of the year. Charts of this type can easily be

    developed for all parts of the polar, arctic, and subarctic regions and

    should be made available for the planning of operations.

           

    Palmer W. Roberts



    Unpaginated      |      Vol_IIA-0294                                                                                                                  

    Arctic Surveying

    EA-I. (Ralph W. Woodworth)

    ARCTIC SURVEYING

           

    CONTENTS

    Page
    Introduction 1
    Preparation s for Arctic Surveys 2
    Local Transportation 3
    Surveys 4
    Geodetic Control Surveys 4
    Astronomical Observations 4
    Base-line Measurements 5
    Horizontal Control 5
    Level Net 5
    Station Marks 5
    Topographic Surveys 6
    Hydrographic Surveys 7
    Hydrography 7
    Tides 9
    Magnetics 9
    Conclusions 10
    Bibliography 10



    Unpaginated      |      Vol_IIA-0295                                                                                                                  
    EA-I. Woodworth: Surveying

           

    LIST OF FIGURES

    Page
    Fig. 1 Alaska triangulation net 10-a
    Fig. 2 Alaska hydrographic surveys 10-b



    001      |      Vol_IIA-0296                                                                                                                  
    [EA:I. Ralph W. Woodworth]

           

    ARCTIC SURVEYING

           

    INTRODUCTION

            The special problems encountered in surveys of the land and water areas

    of arctic regions are due to the raw or undeveloped nature of the country. The

    land routes of communication, except in the vicinity of the larger settlements,

    are primitive and the meteorological conditions are rigorous. Both combine

    to limit activities, at present, to less than six months of the year. Winter

    work is reduced to a minimum.

            Surveys in the Arctic are not difficult to accomplish. The subzero tempera–

    tures are uncomfortable and the danger element is, of course, always present.

    With careful planning, a knowledge of the country, experience with the limita–

    tions of the various types of transportation, and the elimination of unneces–

    sary risks, operations may be carried out safely and efficiently although at

    high cost.

            The over-all success of a project is dependent to a considerable degree on

    the detailed plans made for the project, as under the comparatively harsh condi–

    tions of the Arctic, nothing may be left to chance. The selection of proper

    transportation equipment is perhaps the greatest single factor that will con–

    tribute to the success of a mission.



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            Surveys in subarctic regions are planned and accomplished in much the

    same way as surveys in the temperate zones. These areas are more accessible

    and weather conditions are milder than those of the Far North. Field methods

    and instrumental equipment are similar to those used in the temperate regions.

           

    Preparations for Arctic Surveys

            To achieve maximum efficiency in the short field season, the following

    preparatory steps should be taken.

            1. Prepare comprehensive and detailed plans to cover every phase of

    supply, administration, and operation well in advance of the beginning of the

    project.

            2. Procure, test, and condition suitable rugged equipment and instruments

    with spares of all items and a generous supply of spare parts.

            3. Insure and adequate supply of communication equipment.

            4. Ship the equipment to arrive well in advance of probable needs.

            5. Prior to departure from the continental base, instruct all personnel in

    the nature of the proposed su s rveys, the character o the country, the special

    care required for the equipment, and the methods of operation.

            Procurement, particularly for the specialized items, should be instituted

    a year in advance of operations. Checks must be made to insure that items that

    cannot be procured in the Arctic are in the hands of the survey party at least

    two months before departure.

            Personnel should be transported from the continental area to the Arctic

    by airplane on the following schedule which may be modified as weather conditions

    permit.



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            1. Mid-January: liaison group to complete preliminary field arrangements.

            2. Early February: astronomic groups.

            3. Mid-February: chief of party and staff, plus geodetic (triangulation

    observing) groups.

            4. Early June: balance of party.

            Good organization requires that each subparty shall be as nearly self–

    sufficient as practical; that one reliable Eskimo familiar with the country

    shall be included with each unit; that each observing group shall include an

    extra observer; and that the specialists, the heavy equipment, labor pool, and

    emergency transportation shall be under control of the headquarters group.

            Base camps should be selected at least two years in advance and supplemen–

    tal camps one year.

            Plans must provided that mobile parties carry a full allowance of rations,

    sleeping bags, and sample communication equipment. Radio schedules must be set

    up and these schedules maintained.

           

    Local Transportation

            Because of the undeveloped nature of the country, local field transporta–

    tion requires limited support of both small and large airplanes, bulk-hauling by

    tractor or sledge trains, and employment of small amphibious-type tracked vehicles.

    Wheeled vehicles, unless ski-mounted, are nearly useless.

            Dog teams are useful in an emergency. The light pay load and the neces–

    sity of carrying or securing food for the animals definitely limit their value.

    The dog sledge is a very desirable article of equipment and may be trailed

    behind weasels” or jeeps.

            Ship or launch transportation in the Arctic is limited to the few months of

    open water.



    004      |      Vol_IIA-0299                                                                                                                  
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    SURVEYS SURVEYS (delete underlining)

            Surveys in the Arctic comprise geodetic control surveys for the deter–

    mination of geographical positions and elevations for use in charting and

    mapping; topographic surveys from aerial photographs; and hydrographic surveys

    for the determination of depths of water for navigation.

           

    Geodetic Control Surveys

            Geodetic control surveys include astronomical observations for determina–

    tion of the position of the starting point and initial azimuth; base-line measure–

    ments; and horizontal observations of directions for extension of triangulation

    or traverse.

            Astronomical Observations . Where possible, the starting point and initial

    azimuth should be determined with precision. This can be done with standard

    methods and equipment. Azimith may be obtained with a direction theodolite.

    Where weight of instruments is a factor, satisfactory observations of latitude

    and longitude may be obtained, using the “equal altitudes” method and the pris–

    matic astrolabe.

            The best time for observations, especially above the Arctic Circle, is

    during the hours of darkness in the early spring or late fall. Spring obser–

    vations are made ordinarily in less time and more economically than fall obser–

    vations because the skies are clearer and radio reception is better due to the

    absence of the northern lights, although the temperature is lower.

            Above latitude 60°, special care must be taken in order to secure a satis–

    factory value for azimuth because of the close spacing of the meridians. The

    method outlined Hoskinson and Duerksen (7) for observations of this type will

    yield excellent results.



    005      |      Vol_IIA-0300                                                                                                                  
    EA-I: Woodworth: Surveying

            The instruments used are sparingly oiled with a very fine watch oil and

    tested to −50°F. in a cold chamber. Between observations they are placed in

    unheated storage to prevent condensation and subsequent fogging of the lenses

    and freezing of bearing surfaces. Glycerin rubbed on contact points will

    effectively prevent freezing.

            Base-line measurements are more easily made over flat ground or the flat

    ice of lakes or lagoons with the line laid out in the direction of the pre–

    vailing wind. First-order accuracy may be obtained with standard methods.

    Stakes should be steam-jetted into the ice or ground using a portable boiler.

            Horizontal control in the Arctic is extended by triangulation methods.

    Triangulation is faster than traverse and will produce more points for the

    same amount of effort.

            Standard triangulation observing methods as given by Hodgson (6) and in

    another manual of the U.S. Coast and Geodetic Survey (15) have been found

    to be the most economical methods for daylight work in the Arctic.

            The observing period begins when there is sufficient light to warrant plac–

    ing the observing groups in the field and ends when the combination of spring

    thaw, making travel dangerous, and melting of snow, which produces excessive

    refraction, render operations uneconomical. North of the Arctic Circle this

    period extends, normally, from February to May or June.

            Level Net . Except for the lines of spirit levels along the Alcan Highway

    and the Alaska Railroad, elevations have been determined by trigonometric

    leveling. Such elevations may at times be subject to errors due to excessive

    vertical refraction varying over the period of the level run.

            Station Marks . In subarctic regions, including the Aleutian chain, stations

    006      |      Vol_IIA-0301                                                                                                                  
    EA-I. Woodworth: Surveying

    are marked with brass disks set into a drill hole in rock or into a concrete

    block buried in the ground. In the higher latitudes where the permafrost

    is close to the surface, the best marks are brass disks brazed to an iron

    pipe steam-jetted into the ground.

           

    Topographic Surveys

            Aerial photographic methods provide the best means of obtaining topo–

    graphic data. Ground methods are useful only for fill-in. The photographs

    are controlled by a tie between ground features and stations established by

    triangulation.

            Photographic and field inspection operations are confined to a very short

    period of the year. To secure accurate information, the ground must be photo–

    graphed and the field inspection made when snow is at a minimum and the shore

    line is clear of ice. In the Far North the best time has been found to be

    during July and August and in the subarctic regions in the spring or late fall.

            The long shadows cast by the sun interfere with and often obscure detail

    on slopes. This condition is minimized by taking photographs, where possible,

    when the sun is at its maximum declination but there is no satisfactory

    solution to the problem. Elevations supplemental to those obtained by leveling

    may be obtained by means of the phototheodolite.

            The best and quickest method of spotting control for the field inspection

    parties is to furnish them with low- or medium-al [ ?] titude verticals and obliques

    in the vicinity of the stations. Methods which involve the use of ground

    transportation may be used when more economical. When topography is not car–

    ried out simultaneously with control, each station must be inspected on the

    ground.



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    Hydrographic Surveys

            Hydrography . Standard field methods, as outlined by Adams (1), are

    suitable for arctic surveys. The principal problems are not technical in

    nature but have to do with the full utilization of the short working season

    and the selection of the best available equipment. The plans should provide

    that all preliminary work, such as preparation of the sheets and overhaul

    and conditioning of the equipment and instruments, will be completed well

    in advance of the probable date of arrival of open water, so that hydro–

    graphic operations may be commenced without delay.

            The hydrographic signals are built and located [ ?] by the triangula–

    tion part as it progresses. On a resurvey they may be located by graphic

    means or photogrammetric methods, either of which yields satisfactory results.

            Several types of boats have been used in the Arctic. The Navy rearming

    boats are 35-foot diesel-powered single-screw wooden launches with enclosed

    cabins and are capable of 12-15 knots speed. The landing craft are of various

    types. The LCVP (Landing Craft Vehicle Personnel), a diesel-powered single–

    screw wooden boat with open cockpit and ramp bow, is capable of 8-12 knots

    speed, but is a very wet boat in a seaway. The LCM (Landing Craft Mechanized),

    a 50- or 56-foot diesel-powered, twin-screw, steel boat with open cockpit

    and ramp bow, is capable of 8-10 knots, and is a reliable craft.

            Modifications to fit the boats for efficient use include: construction of

    a shelter for the hydrographic crew on open-cockpit boats; removal, in some

    cases, of the top of the ramp flush with the coaming of the boat to improve the

    visibility; installation of strainers designed to keep slush out of the

    engine on raw water cooling systems, or replacement of this type with keel

    condenser systems; installation of metal sheathing along the water line for

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    EA-I. Woodworth: Surveying

    wooden boats in order to protect the hull from “young” ice; replacement of

    Au: OK? the magnetic compass with a magnesyn-type compass; and application of a coat

    of orange paint for easy identification. In addition to hull and engine

    modifications, provision must be made for installation of the sounding and

    radio apparatus. Each boat should be fitted with two Fathometers, an out–

    board and inboard projector, and a two-way radio. Emergency rations and

    sleeping bags for all personnel should be carried at all times.

            The best method of developing an area is by lines parallel to the beach.

    Such a system provides maximum coverage with least cost. Every effort should

    be made to complete one area before progressing to the next. For maximum

    safety, boats must work in pairs and remain in close proximity, one sound–

    ing out an offshore line while the other works along an inshore line. A

    fully equipped spare launch should be available in each camp.

            The launches should never enter a lead in the ice, but if caught, the

    landing craft should pick out a shelving section of ice and allow the boat

    to be pushed upon it. Conventional boat types should tow a light dory and

    carry two outboard motors.

            When ice is drifting on the shore, it will ground in water deeper than

    the draft of the launch so that generally the boat may find open water close

    to shore. In open ocean areas, if the wind picks up, the launches must get

    through an inlet before the ice or breakers close it.

            Experience to date has indicated that the period from mid-July to mid–

    September is the most suitable for hydrography in arctic water, but this

    period is subject to wide variations from year to year. In the Aleutians,

    the period from May to October is best.



    009      |      Vol_IIA-0304                                                                                                                  
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            Tides . The tide gages must be established prior to commencement of

    hydrography. The types in common use are described in a special publication

    of the U.S. Coast and Geodetic Survey (16). The portable automatic gage is

    the only practical type for these areas unless a plain staff gage is estab–

    lished for a short series of observations.

            At Point Barrow, the normal tide is small — a daily range of less than

    a foot. The wind effect is much greater and has been recorded as reaching

    3 feet. Winds blowing along the coast northerly and easterly from Point

    Barrow lower the water level at Point Barrow, while winds from the opposite

    direction raise it.

            Because of the small range of tide, gages are visited frequently and

    the marigrams changed every 48 hours. The staff is checked at each visit

    and revealed when damage is suspected.

            If necessary to build a gage on the ice, it may be done in the follow–

    ing fashion: Erect a plain staff in a suitable position, make a hole through

    the ice, and insert a pipe (4 inches in diameter or larger) filled with oil.

    Pass a wire through the pipe and anchor it to the bottom, lead the free end

    through a sheave on or near the top of the staff and down in front of the

    staff. Secure a weight to it which will serve to keep the wire taut and to

    indicate the depth. As the tide rises and falls the weight will register

    on the graduated staff.

            Magnetics . In subarctic regions where the magnetic field is sufficiently

    strong to orient the needle quickly, standard methods, as outlined by Hazard (5),

    may be used.



    010      |      Vol_IIA-0305                                                                                                                  
    EA-I. Woodworth: Surveying

            In the Arctic no comprehensive magnetic surveys have been made. It is

    doubtful if any great coverage of this region may be made until air-borne

    operations are feasible. In this area, the horizontal component (declination)

    of the earth’s magnetic field is weak and displays complexities and variations

    that are neither well mapped nor well understood.

            Instruments must be especially calibrated for the magnetic latitude when

    used in high arctic regions. Observations are impeded by the length of times

    required to dampen the oscillations of the needle and by frequent unpredict q a ble

    magnetic storms.

           

    Conclusions

            Progress in surveying and mapping in the Arctic will be accelerated by the

    increasing interest in the region, by increased efficiency due to the probabl y e

    introduction of more efficient methods of surveying such as Shoran, and the

    longer field season that will result as knowledge of the region increases.

            The att c ac hed sketches (Figs. 1 and 2) show graphically the progress that

    has been made by the U.S. Coast and Geodetic Survey in Alaska in the fields

    or triangulation and hydrography through 1948. It is apparent that although

    the progress during the last 50 years has covered a large proportion of the

    most accessible part, a vast area still remains to be done.


    BIBLIOGRAPHY

    1. Adams, K.T. Hydrographic Manual . Wash., D.C., G.P.O., 1942. U.S. Coast &

    Geodetic Surv. Spec.Publ . no.143. Rev. (1942) ed.

    2. American Society of Photogrammetry. Manual of Photogrammetry . N.Y.,

    Chicago, Pitman, 1944.



    010a      |      Vol_IIA-0306                                                                                                                  

    Fig. 1



    010b      |      Vol_IIA-0307                                                                                                                  

    Fig. 2



    011      |      Vol_IIA-0308                                                                                                                  
    EA-I. Woodworth: Surveying


    3. k Drygalski, Erich von. Die Deutsche Südpolar-Expedition. Ber lin, Mitller,

    (1902-03) 3v. in 2. Berlin. Univ.Inst. für Meeresk. Veröff . H.1-2, 5.

    4. Great Britain. Royal Air Fo r ce. Empire Air Navigation School. Report no.45/24.

    2 North Polar Flight of “Aries. ” 1946. 10 pts. Especially pt.10,

    sect.5, “Terrestrial magnetism and magnetic compass in the Arctic.”

    5. Hazard, D.L. Directions for Magnetic Measurements . Wash., D.C., G.P.O., 1921.

    U.S. Coast & Geodet.Surv. Spec.Publ . no.166.

    6. Hodgson, C.V., Manual of First-Order Triangulation . Wash., D.C., G.P.O., 1926.

    Ibid . no.120.

    7. Hoskinson, A.J., and Duerksen, J.A. Manual of Geodetic Astronomy. Determina–

    tion of Longitude, Latitude, and Azimuth
    . Wash., D.C., G.P.O., 1947.

    Ibid . no.237.

    8. International Boundary Commission. Joint Report Upon the Survey and Demarca–

    tion of the International Boundary Between the United States and Canada

    Along the 141st Meridian from the Arctic Ocean to Mt. St. Elias
    .

    Wash., D.C., 1918.

    9. Leffingwell, E. de K. The Canning River Region, Northern Alaska . Wash., D.C.,

    G.P.O., 1919. U.S.Geol.Surv. Prof.Pap . 109.

    10. Madill, R.G. “The search for the North Magnetic Pole,” Arctic , vol.1,

    T pp.8-18, Spring, 1948.

    11. Mussetter, William, Manual of Reconnaissance for Triangulation . Wash., D.C.,

    G.P.O., 1941. U.S.Coast & Geodetic Surv. Spec.Publ . no.225.

    12. Rappleye, H.S. Manual of Geodetic Leveling . Wash., D.C., G.P.O., 1948.

    Ibid . no.239.

    13. Sverdrup. H.U. “Magnetic, atmospheric-electric, and auroral results, Maud

    Expedition, 1918-24,” Carneg.Inst.Wash. Publ . no.175, vol.6, pp.309-524,

    1927.

    14. Swainson, O.W. Topographic Manual . Wash., D.C., G.P.O., 1928. U.S.Coast &

    Geodetic Surv. Spec.Publ . no.144.

    15. U.S.Coast and Geodetic Survey. Manual of Second and Third Order Tria gn ng ulation

    and Traverse . Wash., D.C., G.P.O., 1929, Ibid . no.145.

    16. ----. Manual of Tide Observations . Wash., D.C., G.P.O., 1935. Ibid . no.196.

           

    Ralph W. Woodworth



    Unpaginated      |      Vol_IIA-0309                                                                                                                  

    Highways, Bridges and Protection from Ice Damage

    EA-I. (Angelo F. Ghiglione)

    HIGHWAYS, BRIDES, AND PROTECTION FROM ICE DAMAGE

           

    CONTENTS

    Page
    Location 1
    Bridges 2
    Road Construction 5
    Maintenance 7
    Effluent Seepage Icing 9
    Stream and River Icing 11



    Unpaginated      |      Vol_IIA-0310                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

           

    PHOTOGRAPHIC ILLUSTRATIONS

            With the manuscript of this article, the author submitted

    16 photographs for possible use as illustrations. Because of the high

    cost of reproducing these as halftones in the printed volume, only a

    small proportion of the total number of photographs submitted by all

    contributors to Volume I can be used, at most one or two of the illus–

    trations accompanying each paper, and in some cases none. The selection

    of halftone illustrations for Volume I must await further progress in

    publishing plans, for the number that can be used will be determined by

    the publisher, and the choice of those used should be made in conjunction

    with a representative of the publisher. All photographs are, therefore,

    being held at the Stefansson Library until a selection can be made.



    001      |      Vol_IIA-0311                                                                                                                  
    EA-I. (A. F. Ghiglione)

           

    HIGHWAYS, BRIDGES, AND PROTECTION FROM ICE DAMAGE

            The accumulated experiences in Alaska of a generation of engineers,

    construction men, and prospectors are properly reflected in the present

    practices and operations of the Alaska Road Commission. The most workable

    location, construction, and maintenance procedures for the near-arctic and

    subarctic conditions encountered have been evolved through years of practice.

           

    Location

            Most of the road planning in Alaska in pioneer location through virgin

    country, which has not been surveyed or settled upon, and the route is,

    therefore, not appreciably controlled by other than construction and sub–

    sequent maintenance considerations. In addition to the usual location criteria

    of conformance to the general road system planning, shortest route, standard

    alig h nment and grades, reasonable economic design, and safety of traffic,

    certain very important regional requirements must be considered.

            Permanently frozen ground, or permafrost, underlies approximately

    80 per cent of Alaska. Where at all possible, road location should avoid

    these areas and the high construction and maintenance costs incident thereto.

    The locating engineer soon learns to identify frozen ground by the type of

    foliage and moss supported upon it.



    002      |      Vol_IIA-0312                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

            A prime consideration is the development of locations on the south,

    rather than the north, slopes of hills and mountain ranges. Several reasons

    for such southerly exposure of location, all directly resulting from the

    appreciably greater heat effect of the sun, are as follows. First, the

    f g round is more likely to be thawed and free from permafrost. Second, the

    construction will have the advantage of an earlier spring thaw and later

    fall freeze-up together with more rapid thawing of the ground as it is

    worked and exposed. Third, the maintenance problems are reduced [ ?]

    by the lighter snows, less slippery surface, less winter ground ice forma–

    tion, and earlier spring thaws.

            Wet sidehills or slopes, which indicate possible effluent seepages,

    are avoided since spalling of slopes and major slides are to be expected

    and winter ground icing will normally result. Likewise, the location must

    be kept sufficiently above the known stream icing elevations of all streams

    and rivers, either marginal to or crossing the line.

            Other precautions essential toward minimizing the winter maintenance

    problems include avoiding through cuts which induce drifting, and planning

    slightly raised or fill sections which tend to be swept clear of snow.

    Normal construction where permafrost cannot be avoided is to use an unbalanced

    fill. Minimum grades and curvature are utilized to reduce winter maintenance

    and increase safety of winter traffic operation.

           

    Bridges

            Bridge locations in subarctic areas require the additional consideration

    of winter ground icing possibilities, stream ice break-up and flow, and the

    channel-shifting to be expected of most glacier streams. In addition, numerous

    003      |      Vol_IIA-0313                                                                                                                  
    EA p -I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    glacier rivers in Alaska are subject to extreme flash floods from the

    bursting of glacier-dammed lakes or streams. Glacier floods in large rivers

    such as the Nizina, Knik, and Kenai irregularly raise those rivers as much

    as twenty feet and cause serious ice flow, bank erosion, and drift problems.

    Such floods may occur in summer or in winter and, in the latter case, do

    considerable damage by carrying heavy broken river ice against the bridges,

    in addition to ice brought down from the glaciers, and ordinary drift com–

    posed of trees, stumps, and other debris.

            The bridge locations, to cope with the above conditions, are preferably

    chosen well in advance of the road location and act as control points for

    the route. A narrow crossing where the river is confined in one channel

    by geographical features is preferred and a high level crossing, supported

    by geographical features, is similarly desirable. Such a location would

    naturally eliminate many usually maintenance problems resultant from the

    above-listed subarctic conditions. In actual practice, however, it is

    usually necessary to accept less than the ideal crossing, since the economics

    of the over-all route location seldom justify allowing the bridge crossing to

    control the line.

            Bridge design must provide a minimum of restriction to river flow and

    sufficient height to clear floods, ice flow, and winter ground and stream

    icing formations. As a rule, clear spans are more satisfactory than trestle–

    type structures, and mid-channel piers are undesirable since special icebreakers

    and protective structures must nearly always be provided. On wide, flat,

    glacier stream crossings where channel shifting is prevalent, the over-all

    bridge length can often be reduced by utilization of dikes, wing dams, and

    other channel control structures of restrict the flow to a single opening.

    004      |      Vol_IIA-0314                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    Such bank protective measure are costly and require continual maintenance,

    but are often found economically justified by saving in cost, resulting

    from decreased length of the bridge structure required.

            Standard steel bridges have been widely employed for Alaskan roads.

    These bridges are mostly simple truss and girder spans, though arches, sus–

    pension bridges, and cantilever designs are freely used for special crossings.

    Timber T t restles and truss spans have been used extensively in the past but

    are being replaced with steel as rapidly as possible. The timber trestle is

    used for small crossings and on secondary roads.

            Concrete is used for bridge seats, footings, and some abutments, but is

    seldom used for spans or piers because of the comparatively high costs involved.

    No cement is produced in Alaska and the freight costs to interior Alaska for

    this bulky material amount to several times its value. Most gravel and sand

    available for concrete aggregate requires extensive washing and screening to

    remove glacial silt which predominates in the deposits. In the isolated

    locations common to most Alaska bridge construction, these factors, together

    with the additional plant and skilled tradesmen required for the aggregate

    preparation, form erection, concrete mixing and placing, and heating during

    cold weather placing, make concrete construction exceptionally costly. By

    comparison, steel structures can be easily handled, freighted, and erected with

    a relatively small plant setup. Steel structures in the North do not deterio–

    rate appreciably as compared to similar structures in southern moist climates.

    Concrete, on the other hand, deteriorates faster in the North due to the

    numerous cycles of extreme freezing and thawing.

            Piers for the bridges in Alaska are predominantly of the steel “H”

    piling bent type which have been developed by the Alaska Road Commission and

    005      |      Vol_IIA-0315                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    proved very satisfactory. Their cost is considerably less than comparable

    concrete piers, the permanence is equal thereto, and the comparatively

    simple handling and erection facilitates use in isolated locations. Their

    cost is relatively low since they require none of the expensive excavation,

    form work, cofferdam or caisson construction, or underwater work common to

    concrete piers. In addition, they are well adapted to use in frozen ground

    and can be placed as easily in winter as in summer. This factor is impor–

    tant in Alaska where most bridge work is accomplished in the winter when

    concrete operations require costly heating measures.

           

    Road Construction

            The construction of roads in Alaska involves special problems and is

    limited, in general, to the summer season by the frozen ground and the

    extreme cold temperatures of the winters. This restriction results in

    long periods of idle equipment, seasonal employment of crews, and increased

    costs as mentioned above. Bridge work is usually scheduled for winter con–

    struction. This is done in order to provide longer employment for key

    personnel and to provide utilization of the otherwise idle equipment.

    Other measure for reducing costs resulting from the limited seasonal con–

    struction period include winter freighting of supplies and materials to

    advanced construction sites while frozen rivers and swamps aid rather than

    hinder such operations, winter camp erection, and concentration of equipment

    overhaul in the winter months.

            Under normal conditions, the construction methods and equipment used

    in Alaska are the same as those generally employed on large-scale road

    construction projects in the United States. Discussion will, therefore,

    006      |      Vol_IIA-0316                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    be limited to the problems particular to the North where frozen ground is

    one of the biggest obstacles to road construction. The swamp-covered

    permafrost in Alaska is termed “tundra” and is generally a flat or rolling

    terrain on which a thick moss insulates frozen ground beneath the surface.

    The surface, however, thaws unevenly during each summer, and this produces

    a continuous surplus of water. The moss and grass prevent adequate drainage

    so that the water forms small pools and the frozen subsurface retards runoff

    of this water, with the result that in the summer the ground is very swampy

    and soft, even on relatively steep hillsides. The wet soil, practically

    suspended in water, interferes with the operation of regular road-building

    equipment, and the ice or frozen ground just beneath the wet cover impedes

    grading operations.

            The best procedure in such cases is to avoid disturbing the equilibrium

    maintained by nature between the factors in the permafrost province, known

    as the thermal regime. Any construction operation which changes or disturbs

    this thermal regime will be subjected to the forces of nature as they endeavor

    to reestablish this equilibrium. Climatic conditions and geologic changes may

    also affect the thermal regime and, thereby, result in either the degradation

    of aggradation of the permafrost. Where at all possible, therefore, fill

    sections are used over frozen ground — the fill placed with the least possible

    disturbing of the moss or overburden. Where thawing has made the area swampy,

    it is general practice to place a corduroy mat for additional protection and

    support.

            Where the topography requires cutting into frozen ground, the work may

    have to be programmed over several seasons to permit progressive thawing as

    the exposed surface is worked off. Drilling the blasting of permafrost, as

    007      |      Vol_IIA-0317                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    in the case of rock, is resorted to in some cases in order to accelerate

    breakdown of the impermeable material.

           

    Maintenance

            Summer maintenance of roads in the northern regions of Alaska requires

    very much the same procedures as used in the Midwestern States. After the

    spring thaw the roads dry out and become dusty, even though frozen ground

    may be only a few feet below the grade. Particular local problems of

    heaving, sliding, or subsiding ground, resulting from the uneven thawing

    of the underlying frozen ground, require continual maintenance attention

    and are quite common. Corrective measures include removal of slide material

    or placing of additional surfacing material to reestablish uniform vertical

    alig h n ment.

            Brush cutting, ditch and culvert cleaning, spot graveling, and other

    usual maintenance requirements are of necessity concentrated in the summer

    working season. In addition, all possible preliminary steps toward facili–

    tating winter maintenance are taken. Such measures include placing culvert

    stakes and snow takes of sufficient height to be discernible above snowdrifts

    to aid in locating the culverts and the edge of the road when thawing or

    plowing; placing of snow fences and ice fences where know drifting or

    icing occurs; flattening of the road crown in the fall to minimize danger

    of sliding on icy roads; and building up stockpiles of sand and cinders

    for winter surface sanding.

            In the consideration of winter road maintenance, and Alaska Road

    Commission has of necessity developed methods of preventing and coping with

    winter ground ice formations that endanger highways and highway structures,

    008      |      Vol_IIA-0318                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    and constitute a serious hazard to normal traffic flow. Such ice forma–

    tions are locally known and described throughout Alaska as “glaciers”

    and any other designation would be confusing to the average maintenance

    man. However, the term is incorrectly applied and since true glacial

    conditions are seldom encountered on road maintenance, the term will be

    used only when correctly applicable to masses of snow-formed ice. In this

    article, winter ground ice formations particularly affecting winter highway

    travel will be referred to as “icing.” Icing results from the successive

    freezing of sheets of overflowing water into masses of ice attached to the

    ground. For road maintenance considerations, these ice formations are

    classified into two general types — the effluent seepage type and the river

    or stream type. Ground icing of the effluent seepage type is experienced

    throughout most of Alaska while the river or stream type is prevalent only

    in the interior as differentiated from southeast and south-central Alaska.

            As would be expected, the actual formation of the ice masses varies

    unpredictably with the ground, water, and weather conditions. The severity

    of the winter, the amount of snowfall and whether it falls early in the

    season or late, and the nature of the season prior to the freeze-up, whether

    wet or dry, all comprise contributing factors toward the resultant icing

    possibilities. From past experience, certain generalities as to these

    factors have been deduced and may be briefly summarized as follows:

            ( a ) A rainy season prior to freeze-up will increase the ground-water

    flow in winter and usually cause more and heavier icing.

            ( b ) An early heavy snow will tend to insulate the ground and minimize ice

    formation. Conversely, prolonged freezing weather with little snow results

    in considerable icing.



    009      |      Vol_IIA-0319                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

            (c) A severe winter with long periods of extreme cold may tend to

    freeze back and stop the flow and formation of seepage-type ice but will

    increase the formation of the stream and river type. The reverse is

    generally true of mild winters.

            These generalities cannot be considered infallible since various com–

    binations of the conditions may produce opposite results. As a result,

    methods of controlling the ice have been developed both as preventative,

    where possible to forecast probable formations, and as control measures

    where the ice forms infrequently or unpredictably.

           

    Effluent Seepage Icing

            The effluent ground seepage ice is the predominant form to be coped

    with in winter maintenance operations in Alaska. When relatively warm

    ground seepage meets the surface of a highway-cut slope in summer, it

    normally may evaporate, flow down the slope and into the regular drainage

    ditches, or may continue to flow just under the surface. However, in the

    winter, with continued freezing temperatures, this flow freezes soon after

    exposure to the air and forms successive l ev ay ers of ice which build up to

    many feet in thickness or until hydrostatic equilibrium is reached. Since

    this type of ice normally forms on sidehill cuts, the resultant sloping ice

    surface built into the road increases the danger to traffic by crowding it

    to the outer edge and tilting it toward the outside at increasingly steeper

    slopes. This type of icing, besides building to many feet in depth, often

    forms slopes too steep to permit passage of any kind of traffic.

            A relatively inexpensive and very workable method of controlling this

    type of icing has been developed by the Alaska Road Commission and has proved

    010      |      Vol_IIA-0320                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    so successful that its use has spread throughout the Territory and into

    Canada where similar problems occur. Termed “ice fencing,” this method

    employs the principle of damming of the seepage and controlling its freezing

    before it reaches the road. Since the actual head of water to be diverted

    is never more than the depth of the seepage film, the term “dam” is mis–

    leading and the actual fence used may be of light temporary construction.

            In operation, the ice fence is placed as soon as icing is observed, or,

    in cases of annually repeating ice, may be placed before the freeze-up.

    The fence consists of wire netting on pos e t s to which has been fastened to

    a layer of canvas, roofing paper, or similar relatively impervious material.

    The posts may be buried in the ground, if placed prior to the freeze-up,

    may be frozen in holes picked into already formed ice, or may be temporary

    tripods. The wire netting used is either fish-trap wire, chicken wire, or,

    in some instances, standard slat-type snow fencing. The resultant fence,

    with impervious facing for diverting the seepage, need only be of sufficient

    strength to withstand the local winds. It will actually be increasingly

    stabilized by the ice as the thickness of the controlled icing develops.

            The ice fence is placed between the seepage and the road and actually

    controls the ice by diverting the flow parallel to the road until it freezes.

    The resultant vertical wall of ice may build up to considerable depth and

    require a second and sometimes a third lift of the fence during the winter.

    These fences may have proved very effective in keeping ice from forming on

    the roads and are especially preferred to other control methods since only

    infrequent attention of the maintenance crews is required.

            While the ice fence has simplified control of forming ice, it is still

    possible, in some instances, to avoid the icing problem entirely by striking

    011      |      Vol_IIA-0321                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    closer to the source. Interception ditches, graded to pick up the seepage

    before it reaches the road out and to divert it into other drainage channels,

    are possible. This type of control can be used effectively where the ground

    water flows near the surface and can be intercepted at some distance from

    the road.

            Similar interception ditches to collect and channel the seepage flow

    have been effective where such concentrating of the water preserves suffi–

    cient latent heat to keep it from freezing until the water has passed through

    the road drainage structures. While icing will probably still occur, it will

    be below the road and of no danger to traffic. An added measure to insure

    operation of this type of diversion consists of covering or insulating the

    channeled flow against rapid freezing in order further to delay the icing.

    A practical method consists of covering the ditch with brush of sufficient

    thickness to support snow; the snow cover provides considerable insulation.

            Where flow of ground water can be intercepted at some distance from the

    road, it is also possible to cause or control the icing by exposing the

    seepage at a desired location. Clearing and stripping or simply ditching

    may provide sufficient interception and exposure to initiate the icing where

    desired.

           

    Stream and River Icing

            An ice problem more easily coped with is that of stream or river icing —

    formed when the stream freezes to its bed and then continually overflows

    and freezes, forming successive ice layers, in many cases reaching depths

    of more than 20 feet. This type of icing occurs where the stream flows

    over permafrost, and is relatively predictable, since it occurs year after

    year in the same locations. The bridges planned for crossing such streams

    012      |      Vol_IIA-0322                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    must be kept sufficiently high to prevent the overflows from reaching the

    level of the deck with the resultant heavy ice loads built onto the

    structure and danger to traffic. Where overflow has occurred, the bridge

    is not structurally endangered until the period of spring thawing when

    the stream cuts back down to its bed and undermines the ice, leaving many

    tons of it hanging on the bridge. In such cases, it is often necessary to

    remove large quantities of ice from the structure by chopping, thawing and

    cautious use of blasting charges.

            Besides planning high level bridges for icing stream crossings, it is

    important that a clean understructure or clear span be used. As mentioned

    above, use of trestle-type structures is avoided, if possible, since the

    removal of the ice formations from the trestle supports is extremely diffi–

    cult to accomplish without damaging the bracing.

            Where an icing stream threatens to close the o ep pe ning of a large culvert

    or a bridge, the stream may sometimes be kept flowing through the opening by

    channeling and heating. The application of heat to the water above the

    opening tends to delay its freezing until below the highway and also to cut

    out a channel in the already formed ice. The heat may be supplied either by

    means of a boiler through steam pipes laid above or through the opening, or

    more simply by means of a 50-gallon steel drum heater placed on end in the

    channel above the opening. This type of heater is merely a drum with one

    end cut out and in which a fire is maintained by use of oil or wood. Usually

    an infrequent fire, once a day or less, will provide sufficient heat to keep

    the channel open.

            Where icing streams and rivers parallel highways, the principal protec–

    tive measure is again that of building the road sufficiently high to avoid

    013      |      Vol_IIA-0323                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    overflow. Where overflow of the road does occur, continual attention is

    necessary to maintain traffic and to protect the road from subsequent

    washouts during the spring thaw and runoff period. During winter mainte–

    nance of such sections of road, it is necessary to provide a relatively

    flat and level traveling surface for the safe operation of traffic by

    picking wheel ruts, diver g t ing or chan n eling the overflow, and blasting and

    blading the uneven ice. Numerous instances of traffic being maintained

    over long sections of the ice several feet thick without the public being

    aware of its being completely off the road surface have been the result of

    proper maintenance provisions.

            During the spring thaw and runoff, it is essential that culverts be

    thawed open and the streams be controlled in their regular channels as

    quickly as possible. Culvert thawing is usually accomplished by means of

    steam from small truck-mounted boilers. Varying lengths of small-sized

    pipe (usually ½' in.) are connected with sufficient steam hose to permit

    working at considerable distance from the boiler position on the road. The

    pipe is worked through the ice in the culvert as the steam thaws ahead —

    usually starting from the lower or outlet end in order that the melted water

    may escape. It is essential that culvert stakes be set prior to winter

    maintenance in order to facilitate locating frozen culverts for thawing.

    All culverts are staked by the Alaska Road Commission in a uniform manner

    to simplify these operations.

            In some instances the thawing of culverts by the method described above

    is impracticable. Such cases are encountered in extremely long culverts as

    under high fills, in culverts which have had several feet of ice form around

    and above the inlet and, in some instances, also above the outlet, and in

    014      |      Vol_IIA-0324                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    old partially collapsed or deformed culverts through which a straight

    thawing pipe is difficult to handle. Where the failure of such a culvert

    might endanger a large fill or critical section of road, thawing may be

    provided by means of permanently installed thawing pipes. Such pipes of

    relatively small diameter are hung inside the culvert prior to the freeze-up,

    carried out and up to easily accessible locations on each end, and capped

    to prevent plugging by condensation. Any necessary thawing of the culvert

    may subsequently be accomplished by attaching a line from a mobile steam

    boiler to the permanently installed pipes.

            In large fills where the culverts are extremely long, an added precaution

    is sometimes taken by installing a “relief” culvert near the top of the fill

    above the icing height. Such relief culvert will handle spring runoff until

    the lower culvert thaws open.

            The freezing back of thawed culverts during spring operations may be

    partially controlled by use of rock salt — a quantity of salt deposited near

    the culvert inlet in a burlap sack will tend to prevent such freezing until

    the flow of the thawing runoff cuts a sufficiently large opening through

    the ice.

            Where roads are not kept open during the winter and icing has been

    allowed to proceed uncontrolled, a considerable problem for traffic results

    in the spring opening. In extrems cases, such ice has covered sections of

    road several thousand feet in length and to depths exceeding 20 feet. Re–

    moval requires blasting, cutting with tractor and bulldozer, and repeated

    blading as the surface softens through thawing. Sprinkling dirt or ashes to

    accelerate the thawing effect of the sun is effective, and also liberal use

    015      |      Vol_IIA-0325                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    of rock salt will expedite the ice removal. While traffic can be main–

    tained over relatively flat thawing ice, it is sometimes hazardous and

    requires the constant attention of the maintenance forces.

            Numerous other ice problems are encountered in road work in Alaska,

    but are of relatively minor importance and will, therefore, be dealt with

    briefly.

            Ice flow in rivers during the break-up period, known as debacle, con–

    stitutes considerable menace to bridge piers and marginal road structures

    and fills. Protective measures include ice shears, heavy rock riprap, and

    steel piling icebreakers on the upstream sides of the piers. Timber piling,

    as in trestle structures, must be sheeted with metal or planked for full

    width of bend above and below ice line to prevent being cut off by passing

    ice.

            Frost mounding and frost heaving, while deforming the roads in places,

    do not usually constitute serious hazards to winter traffic. Frost mounds

    have, in instances, upwarped the surface as much as six feet in the middle

    of the road and have again subsided leaving no apparent damage. The opposite

    action occurs occasionally where roads are located over permafrost containing

    ice lenses or ice veins. The uneven melting of the ice or the shifting of

    underground water channels may cause serious subsidence of many feet over

    relatively short periods of time.

            Frost boils, resulting from uneven and accelerated spring thawing, are

    a serious problem to proper road maintenance and result in rough and some–

    times impassable roads. Maintenance procedures include covering with coarse

    pervious gravel, removing the weakened surface material by digging or blasting

    with ditching powder and backfilling with coarse gravel, or by - passing the

    016      |      Vol_IIA-0326                                                                                                                  
    EA-I. Ghiglione: Highways, Bridges, and Protection from Ice Damage

    traffic and permitting the boil to dry up naturally where road width will

    permit.

            With the every-increasing winter traffic flow over the principal

    Alaskan highways, the problems incident to proper and safe maintenance

    operations are becoming of greater importance in the over-all highway

    program. Additional preventive measures are justified both in the initial

    construction planning and in the maintenance improvements such as minor

    changes in alignment and grade. As an accumulated result, the actual daily

    winter maintenance problems are being simplified, the general winter travel

    conditions are being steadily improved, and the highways are being made

    safer for use by the general public.

           

    Angelo F. Ghiglione



    Unpaginated      |      Vol_IIA-0327                                                                                                                  

    Drainage, Flood Control and Beach Erosion in Alaska

    EA-I. (James Truitt)

    DRAINAGE, FLOOD CONTROL, AND BEACH EROSION IN ALASKA

           

    CONTENTS

    Page
    Lowell Creek 3
    Tanana River and Chena Slough 5
    Salmon River 7
    Skagway River 8
    Erosion 10



    001      |      Vol_IIA-0328                                                                                                                  
    EA-I. ( Colonel James Truitt)

           

    DRAINAGE, FLOOD CONTROL, AND BEACH EROSION IN ALASKA

            Degradation of the land mass throughout Alaska is progressing at a

    relatively high rate as the result of water action, despite the fact that

    the major drainage systems are icebound and practically dormant for fully

    50 per cent of the year. In general, the central portion of Alaska is not

    subject to heavy precipitation or torrential rainfall normally associated

    with serious flood conditions. Flooding along Alaskan water courses does

    not conform to the general concept of disastrous floods in that the duration

    and extent of inundation are quite limited. However, the steep gradients

    and resultant velocities of the uncontrolled waters cause serious destruction

    in their path and threaten the establishment of channel changes. Consequently,

    stream bank erosion and flooding are matters of primary concern in the planning

    of all large-scale developments in Alaska.

            The principal Alaskan streams have their sources in the snow and ice

    fields of the surrounding mountains, hence, floods of various magnitudes may

    be expected during the warmest and driest period of midsummer. The intensity

    of this type of flood may vary from a bank-full stage, resulting from an uninter–

    rupted discharge of snow-melt, to out-of-banks flash floods caused by the forma–

    tion of local ice jams or the failure of ice dams at or near the terminus of

    hanging glaciers. Two outstanding examples of such flooding characteristics

    002      |      Vol_IIA-0329                                                                                                                  
    EA-I. Truitt: Drainage, Flood Control, and Beach Erosion

    are noted in the Knik River, discharging into the head of Knik Arm, Cook

    Inlet, and the Copper River which empties into the Gulf of Alaska. Devas–

    tating flash floods are practically annual occurrences on these streams

    and are responsible for serious damage to bridges and other improvements

    in their lower reaches. In 1926, the writer was directed to investigate

    the source of these damaging floods in the Copper River drainage and to

    determine what, if any, steps could be taken to prevent their reoccurrence.

    The source was found to be at the foot of the Skolai Glacier in the head–

    waters of the Nizina River, a tributary of the Copper. In this case, an

    arm of the glacier abuts a vertical rock wall, forming a dam which impounds

    a lake some 5,000 acres in extent. By midsummer, the snow- and ice-melt

    from the glacier fills this basin and when the hydrostatic pressure reaches

    about 120 feet, the gravel base under the ice dam blows out releasing the

    entire lake down a channel where the gradient varies from 7 per cent

    initially to about 2 per cent in the lower reaches. The top o graphy at the

    abutment of the ice dam is such that a spillway and short tunnel through

    the rock wall could be built to relieve this condition. However, such a

    plan could not be recommended since the tunnel would in all probability

    become inoperative because of ice. Furthermore, the high cost of construc–

    tion in this extremely remote locality would have far outweighed the benefits

    that would then accrue. A somewhat similar condition exists at the head of

    the Knik River and there are undoubtedly many other instances that have not

    been investigated or reported.

            Floods in the Salmon and Skagway rivers, in the coastal regions of

    southeastern Alaska, follow a much more conventional pattern, as floods in

    these drainages generally occur in the early spring following heavy rains

    003      |      Vol_IIA-0330                                                                                                                  
    EA-I. Truitt: Drain ing age , Flo o d Control, and Beach Erosion

    and the accelerated melting of the snow cover in their basins.

            A combination of flood causes exists in the case of Lowell Creek a

    mountain torrent which discharges into Resurrection Bay at Seward. Floods

    in this stream are unpredictable. It may flood in the early spring due to

    unusually heavy precipitation, or at any time in midsummer by the release

    of glacial impoundments at its source.

            The Tanana River, in central Alaska, is subject to flooding and dis–

    tributary channeling in the Tanana lowlands above Fairbanks as the result

    of ice jams during the spring break-up. The condition in the Fairbanks

    area is further aggravated by the general movement of the Tanana River

    toward the right limit of its valley floor, due to the fact that the tribu–

    taries from the Alaska Range which form the left limit of the valley have

    extremely steep gradients, and, in consequence, are building up the valley

    floor with heavy detritus, thus forcing the river toward its northern limit.

            Each waterway presents its own characteristic flood pattern. The limited

    development in Alaska to date has only warranted the investigation or the

    a e d option of control measures on a few streams. A brief description of the

    flood-control projects which the Corps of Engineers has been called upon to

    provide in Alaska follows.

            Lowell Creek. This is a Lowell Creek small stream discharging into

    the head of Resurrection Bay at Seward, Alaska. It drains a 5-square mile

    of glacier-covered mountain slopes through a deeply incise s d channel. Owing

    to its extremely steep gradient, it transports immense quantities of glacial

    detritus at flood stage. During ages past, this material has been deposited

    immediately upon release of the stream from the confines of the canyon section

    to form a delta, which now extends seaward from the mountain wall for a distance

    004      |      Vol_IIA-0331                                                                                                                  
    EA-I. Truitt: Drain [ ?] age , Flood Control, and Beach Erosion

    of about 1,200 yards on a slope of 5 per cent. This delta became the

    townsite of Seward, Alaska, and later the southern terminus of the govern–

    ment-owned Alaska Railroad.

            A series of unusually severe floods during the years 1923 to 1926,

    inclusive, caused extended interruption of traffic on the Alaska Railroad,

    with consequent effect on settlements throughout the Alaska Railroad belt.

            The need for control measures on this waterway was apparent, and under

    authority of an Act approved February 9, 1927, the Alaska Road Commission

    constructed a rectangular timber flume, 12 feet wide, 7 feet deep, and

    3,300 feet in length, to convey the debris-laden flood waters from the

    mouth of the canyon across the townsite to tidewater. This improvement

    was completed in 1929 and served adequately until 1935, by which time the

    deposit of solid materials at the outlet of the flume had built up to such

    an extent that free discharge was no longer possible and the flume became

    choked with boulders and gravel during every flood stage. The volume of

    solids transported is indicated by the effect of a flood in October 1935,

    when the flume was completely filled with gravel from outfall to intake, a

    total quantity of 10,000 cubic yards in 11 hours. The actual quantity of

    solids transported considerably exceeded this apparent amount since the

    flume functioned to a limited degree for the initial 3 hours of this 11-hour

    period.

            A revised plan of control was necessary and further studies were made

    by the Corps of Engineers. As a result of this investigation, it was

    decided that the only plan that would insure full protection to the town

    of Seward and the terminal facilities of the Alaska Railroad would require

    005      |      Vol_IIA-0332                                                                                                                  
    EA-I. Truitt: Drainage, Flood Control, and Beach Erosion

    a complete diversion of Lowell Creek from the townsite area. This condi–

    tion could be met most satisfactorily by construction of a low dam across

    the canyon, about 1,500 feet above its mouth, and a discharge tunnel

    2,100 feet in length, through the mountain forming the right limit of the

    canyon. This plan would permit discharge of the flood waters at an ele–

    vation 65 feet above sea level and about 1,000 feet away from any developed

    area, thus providing a disposal site for about seven million cubic yards,

    or a usable life of about 180 years.

            The project was adopted by the Congress in August 1937, completed by

    the Corps of Engineers in 1940, and provides necessary flood protection

    to the community and the terminal facilities of the Alaska Railroad.

            Tanana River and Chena Slough. The Tanana River has its source on the

    northern slopes of the Wrangell Mountains near the Alaskan-Canadian border,

    flows northwesterly about 500 miles, and discharges into the Yukon River,

    140 miles west of Fairbanks. The river closely follows the northern limit

    of the Tanana lowlands, its valley floor, where it has been forced by the

    deposition of heavy glacial debris brought down by tributaries from the

    north slopes of the Alaska Range which form the left limit of the valley.

    The Chena River, a southwesterly flowing tributary of the Tanana, has its

    source on the low divide between the Tanana and Yukon rivers and flows

    through rolling hill country to emerge onto the valley floor of the Tanana

    about 20 miles above its actual confluence with the Tanana River.

            The city of Fairbanks and the military reservation that embraces Ladd

    Field are located in the lowland area between the Tanana and Chena rivers,

    about 10 miles above their confluence. The Tanana River lowland in this

    locality are subject to overflow during the spring break-up, and the security

    006      |      Vol_IIA-0333                                                                                                                  
    EA-I. Truitt: Drainage, Flood Control, and Beach Erosion

    of Fairbanks and other improvements in the vicinity were further threatened

    by the existence of Chena Slough, a distributary of the Tanana, which drains

    from the Tanana at high water stage and flows westerly to join the Chena

    River a few miles above Fairbanks.

            A marked increase in the volume of water carried by Chena Slough with

    each succeeding flood stage in the Tanana River indicated that a flow far

    exceeding the capacity of the Chena River channel at Fairbanks could be

    expected, and there was considerable evidence pointin t g to an eventual

    channel change of the entire Tanana River.

            Pursuant to Act of Congress, June 1936, the Corps of Engineers was

    directed to investigate the condition and determine what action might be

    taken to avert disastrous floods in the Fairbanks area. The investigation

    revealed that the outflow from the Tanana River into the Chena Slough

    channel was through a number of small chutes in a reach between 25 and 30

    river miles above the mouth of the Chena River, and that ice james in the

    Tanana were responsible for enlargement of existing overflow channels as

    well as the creation of new distributaries in this area. The unstable

    condition of the river banks and the length of the reach involved precluded

    consideration of bank stabilization; hence, less conventional methods of

    control were necessary. Field surveys developed that the Chena Slough

    drainage was concentrated against a rock point projecting into the valley

    floor from the north limit at a point about 15 miles east of Fairbanks.

    The Corps of Engineers recommended that a rock-fill dam be constructed across

    Chena Slough at this point and the barrier extended southwesterly as a

    training dike across the valley floor for about 16,000 feet to the right

    bank of the Tanana River, thus collecting and returning all overflows to

    the main river.



    007      |      Vol_IIA-0334                                                                                                                  
    EA-I. Truitt: Drainage, Flood Control, and Beach Erosion

            The plan was adopted and authorized by Congress in 1938. The project

    was completed in 1941 and has provided full protection against flood menace

    from this source. It should be noted, however, that there is no assurance

    against further attacks of the Tanana River along its right limit down–

    stream from the improvement provided.

            Salmon River . Salmon River has its source in the precipitous mountains

    of the coastal range in southeastern Alaska and empties into the head of

    Portland Canal at Hyder on the extreme southeastern border of Alaska. It

    flows through a deeply incised valley generally less than one-half mile

    in width and its total length is about 25 miles. It is fed by numerous

    mountain torrents heading 3,000 to 5,000 feet above sea level in the snow

    fields of the mountain slopes. The gradient of Salmon River is extremely

    steep in its upper reaches and it retains a fall of 30 feet in the final

    mile above tidewater; hence, velocities are capable of developing new

    channels at any flood stage through the unconsolidated materials on which

    the town and port facilities of Hyder are located. Hyder had been frequently

    inundated, and destruction of the town and its port facilities were threatened

    by the encroachment of Salmon River.

            Rapid shoaling at the head of Portland Canal was seriously restricting

    navigation at the head of this waterway. The port of Stewart, British Columbia,

    just across the boundary line, was already deprived of navigable depths and

    a recent change in the trend of the Salmon River at its mouth indicated the

    delta would shortly include the wharf area at Hyder. Corrective measures

    were necessary both in the interests of navigation and the control of floods.

            In January 1931, Congress directed an investigation with a view toward

    008      |      Vol_IIA-0335                                                                                                                  
    EA-I. Truitt: Drainage, Flood Control, and Beach Erosion

    the control of floods. The corrective measures recommended consisted of

    a stone-faced wing dike, 4,400 feet in length, extending from a rock point

    on the left limit of the river above the townsite to a point on the fan

    where the greater slope was toward the right limit of the delta. This

    plan afforded flood protection to the townsite of Hyder and the wharf

    approaches, and also diverted the discharge of debris away from the wharf

    face toward deeper water in the Portland Canal.

            The project was authorized by Congress in 1934, and constructed by

    the Corps of Engineers in 1935. It has afforded the protection desired

    and maintenance costs have been negligible.

            Skagway River. This water course has its source in White Pass, a

    relatively low saddle in the coastal range between northwestern British

    Columbia and tidewater at Skagway. Its steep, narrow valley provided an

    access route into the Klondike during gold-rush days and was later developed

    for the location of the White Pass and Yukon Railway, a narrow gage line,

    110 miles in length, connecting Whitehorse, Yukon Territory, with the

    United States seaport of Skagway.

            The total length of the river is less than 15 miles and it drains an

    area of approximately 125 square miles of mountainous terrain. It discharges

    into the head of Taiya Inlet, and in recent geological time, it has brought

    down sufficient rock waste from the surrounding mountains to fill the head

    of the inlet for a distance of about 3 miles. This deposit of unconsolidated

    material became the site of Skagway but the building process is still in

    progress; hence, the security of all developments in the lower reach of the

    river was threatened at every flood stage.



    009      |      Vol_IIA-0336                                                                                                                  
    EA-I. Truitt: Drainage, Flood Control, and Beach Erosion

            Investigation of the condition with a view toward providing flood

    protection for the Skagway townsite and wharf area was directed by Congress

    in 1935. In response thereto, the Corps of Engineers recommended the con–

    struction of a rock-faced levee along the left limit of the stream, extend–

    ing 6,700 feet downstream from a stable abutment on the canyon wall through

    the townsite area to tidewater, with an 1,800-foot rubble mound breakwater

    extension over the tide flats to deflect the river discharge away from the

    wharves.

            The project was authorised by Congress in 1938 and completed in 1939.

    Further improvements in the interests of navigation by extension of the

    breakwater was subsequently authorized.

            The growing recognition of the strategic and economic importance of

    the Territory of Alaska will undoubtedly result in its rapid development.

    Stream valleys will certainly be adopted as the site of future communities

    and the information that has now been collected and recorded on the flooding

    characteristics of Alaskan streams can be of inestimable value in the planning

    for permanence and security.

            The control of floods will, of course, become a matter of greater concern

    as settlement and development of the Territory increases. However, it is felt

    that future developments will be planned, taking into consideration the flood

    characteristics of adjacent waterways. These conditions were not recognized

    or carefully weighed in the siting of early settlements in Alaska, as

    evidence s d at Seward townsite, laid out on the built-up delta of Lowell Creek,

    where it emerges from the canyon section, and again, in the case of all Tanana

    lowland developments along the right limit of the Tanana River, where continual

    encroachment of the river is indicated.



    010      |      Vol_IIA-0337                                                                                                                  
    EA-I. Truitt: Drainage, Flood Control, and Beach Erosion

            Erosion of the coast line of Alaska is relatively nonexistent. Although

    some beach erosion has occurred at Nome on the Seward Penninsula as the

    result of severe storms, the coast line generally is building up rapidly

    from the discharge of silt-laden rivers and streams. This condition is

    readily noted throughout the entire coast line from the head of Portland

    Canal in southeastern Alaska to the mouth of the Colville River, discharging

    into the Arctic Sea.

            The delta of the Stikine River in southeastern Alaska has practically

    annexed an offshore island to the mainland within the recorded history of

    Alaskan shipping. Shoaling of the tidal waterways at the head of Knik Arm

    has progressed so rapidly that small trading schooners that served trading

    posts in this region as late as 1910 can no longer navigate these waters.

    The extensive de l ta l s of the Kuskokwim and Yukon rivers can be readily noted

    from any map of Alaska, but the deposition of the silt load of these streams

    is not confined to the delta areas, as indicated by the existence of extensive offshore

    bars reaching for many miles from the river mouths in the direction of the

    littoral drift.

           

    James Truitt

    Strength and Uses of Fresh and Salt Water Ice



    Unpaginated      |      Vol_IIA-0338                                                                                                                  
    EA-I. (Ralph Hansen and Kenneth Linell)

    STRENGTH AND USES OF FRESH AND SALT WATER ICE

           

    CONTENTS

    Page
    Uses of Ice in the Arctic 1
    Strength Properties of Ice 3
    General Characteristics of Ice 3
    Published Test Results 4
    Effect of Intracrystal Structure of Ice 4
    Effect of Impurities in Ice 5
    Effects of Horizontal Stratification in Ice 7
    Effect of Vertical Cracks 8
    Temperature during Ice Formation 8
    Residual Stresses 9
    Effect of Temperature during Test 9
    Effect of Rate of Loading on Strength Tests 12
    Effect of Orientation of Test Specimen 13
    Size and Proportion of Test Specimens 13
    Load-Bearing Capacity of Ice 14
    Records of Actual Ice Loadings 14
    Historical Military Rules 14
    Moskatov’s Empirical Method 15
    Elastic Theory Analysis 16
    Preliminary Elastic Theory Ice Thickness Curves 23
    Comments on Elastic Theory Method and Thickness Curves 23
    Effects of Moving Loads 25
    Methods of Increasing Supporting Capacity of Ice 26
    Bibliography 28



    Unpaginated      |      Vol_IIA-0339                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

           

    LIST OF FIGURES

    Page
    Fig. 1 Bearing capacity of old sea ice for airplanes

    with wheels
    16-a
    Fig. 2 Bearing capacity of fresh-water ice for airplanes

    with wheels
    16-b



    001      |      Vol_IIA-0340                                                                                                                  

           

    STRENGTH AND USES OF FRESH AND SALT WATER ICE

           

    Uses of Ice in the Arctic

            The most important use of both sea ice and fresh-water ice in the Arctic,

    in the present and in the past, has been in aid of transportation. The most

    famous journeys of such explorers as Peary, MacMillan, and others were made

    over frozen seas, on foot or with sledge and dog team. In many arctic areas

    frozen rivers, lakes, and bays are regularly used for winter travel between

    land points, frequently shortening distances by many times over those required

    for overland travel. Ice makes possible the passage in winter of tractor–

    drawn supply trains over water bodies, swamps, and bogs which in other times

    of the year would be impassable.

            Even railroads have been constructed on floating ice. The Russians have

    been particularly persistent in developing this type of construction. A rail–

    road line was, for example, constructed on the ice of Lake Ladoga in the siege

    of Leningrad in World War II, supplementing motor truck supply routes also

    laid out over ice. The value of ice in assisting military operations by pro–

    viding relatively easy means of crossing rivers, lakes, swamps, and other water

    areas is obviously very large in arctic areas.



    002      |      Vol_IIA-0341                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

            The ice of the Arctic provides a surface to support floating weather

    and scientific stations, a notable example of which was the Soviet Papanin

    Expedition, which was established on the ice at the North Pole in May 1937,

    and for nearly a year gradually drifted southward, until removed from the

    ice at a point off the coast of East Greenland in February 1938.

            Various possibilities for increasing the structural usefulness of ice

    remain to be explored. A start was made in this direction during World War

    II in an investigation carried out under the direction of Dr. C. J. Mackenzie,

    President of the National Research Council of Canada (4). The object was to

    devise a means of constructing floating airdromes of ice, which would save

    critical materials required in other methods of creating landing facilities.

    The successful prosecution of the war in Europe resulted in abandonment of

    the project, but not before it had been found that by means of an admixture

    of about 14% wood pulp, the compressive strength of ice could be increased to

    1,100 p.s.i. and its tensile strength to 700 p.s.i. Other means for using ice

    for various structural purposes have been suggested but have received little

    or no actual trial.

            Ice serves as a water supply source in the Arctic. In land areas, all

    surface water sources will usually be completely frozen in the winter and the

    only available source of water will be from the melting of ice or snow. In

    salt-water areas, fresh water is obtainable by melting old sea ice; in summer,

    melting of this ice forms pools of fresh water on the surface of the ice.



    003      |      Vol_IIA-0342                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

           

    Strength Properties of Ice

            General Characteristics of Ice . Ice may be described as a highly viscous

    material having characteristics of a solid. Various observers have reported

    that the range of stress magnitudes within which ice is truly elastic is quite

    small. Although it fractures like a brittle material under breaking loads,

    ice will flow or deform gradually under nonfailure loads, the rate of deforma–

    tion under a given stress being higher at higher temperatures. Under favorable

    conditions for “creep,” deformation may be quite rapid. Ice will also melt

    under pressure; the effect is most pronounced with ice temperature at 32° F.

    The pressure required to cause melting increases very rapidly with only small

    drop in temperature below 32° F.

            It will be apparent from these ice characteristics that it is not easy

    to express the action of ice under stress by one or two simple figures. For

    a material such as steel, working stresses may very easily and accurately be

    established in relation to its yield point. For ice the yield point is some–

    what obscure, and is apparently below practical working stresses; as yet, the

    only really useful orientation point on the stress-strain curve is the failure

    point. When a steel structure is designed, material of given characteristics

    is specified with assurance that the actual steel used will vary an insigni–

    ficant amount from the assumed properties. With ice, however, the material which

    Nature has formed must be used, and its strength will vary considerably, in

    accordance with the chance variations of the several strength-influencing factors

    involved. Even cakes of artificial ice manufactured apparently identically

    show wide spreads of results.



    004      |      Vol_IIA-0343                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

            Published Test Results . Ranges of some ice-strength results are shown in

    Table I. These results represent tests under a wide variety of test methods

    and conditions on many types of ice (including artificial ice) and on speci–

    mens of a wide range of shapes and sizes. Most of the figures are individual

    maximum or minimum test values reported by the various investigators (1; 3;

    5; 7; and original data). Except for strengths of single crystals, the minimum

    Table I. Ranges of Ice Strength Test Results .
    Type test Values reported, p.s.i.
    Compressive strength 70-1,800
    Tensile strength 36-223
    Flexural strength 44-311
    Shear strength 39-353

            values should actually approach zero, corresponding to the condition when ice

    is rotting or candled and is able to support virtually no load. Possibly the

    compressive strength values show the greatest range, in part because more

    investigators have used this relatively easy test than the other types.

            Effect of Intracrystal Structure of Ice . When an ice sheet is formed on

    the surface of a body of fresh water, the ice crystals form with their optic

    axes vertical; that is, with their basal planes horizontal, and grow downward

    with the added ice having its basal planes also [ ?] parallel with the ice surface.

    This influences the over-all strength since, as reported by McConnel from his

    study of the way ice yields to stresses, the individual crystal behaves as if

    it consists of an infinite number of indefinitely thin sheets of paper, normal

    005      |      Vol_IIA-0344                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Walt Water Ice.

    to the optic axis, fastened together with [ ?] some viscous substance which allows

    one to slid e over the next with great difficulty. The sheets “offer no resistance

    to bending, but utterly refuse to stretch except, of course, elastically” (9).

    Thus, on the basis of the structure within the individual ice crystals themselves,

    and apart from other structural characteristics, the properties of ice determined

    from tests may be expected to vary according to the direction of orientation of

    the applied stresses between the horizontal and vertical, relative to the

    original surface of naturally formed ice.

            Effect of Impurities in Ice . The presence of relatively small amounts of

    dissolved or suspended matter in water usually results in ice that is weaker

    and/or which deteriorates more readily under the effects of warmer temperatures

    and sunlight. However, additions of considerable amounts , of such materials

    as wood pulp, as noted previously, are reported capable of increasing strength,

    and also may serve to slow up the melting (4).

            In any water body found in nature, there will be found some dissolved

    minerals and other impurities. Sea water at one extreme is an obvious

    example, but even the clearest natural fresh-water body is not without impurities.

    When each ice crystal forms, it tends to reject these impurities, which then

    form a layer of concentrated impurities about the crystal. When adjoining

    crystals meet, the impurities form a layer between the crystals of lower

    melting point than the crystals themselves. This may greatly affect the physical

    properties of the ice even though the amount of impurities is very small.

    Melting will always be g in g at these boundaries between the ice crystals, and at

    a lower temperature than 32° F. Fresh-water ice becomes rotten as thawing,

    006      |      Vol_IIA-0345                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice.

    starting at the inner crystal boundaries, separates the ice into separate

    needles or columns. This ice is said to be “candled.” Thus, as a result

    of this crystal structure in bulk, the physical properties of ice may vary

    widely, especially when its temperature is near the melting point, depending

    on the amount of impurities in the ice, the temperature, the age of the ice,

    and the length of time that near-freezing temperatures have persisted.

            In formation of sea ice, the effect of the salt content is, of course,

    very pronounced. Freezing of the water portions does not begin until a

    temperature of 28.6° F. is reached in undiluted sea water, and the structure

    produced is porous, containing pockets of brine from which solid salt crystals

    begin to precipitate when the ice cools to about 17° F. (8). The structure and,

    consequently, the strength properties of sea ice improve with time, as the

    concentrated brine drains and as the salinity of the ice becomes gradually

    smaller. Newly formed salt-water ice of relatively high salinity is flexible

    and elastic as compared to ice formed on fresh-water bodies (which is charac-

    teristically brittle), and it does not candle. Salt-water ice more than one

    year old is much tougher and stronger than young sea ice, but its surface is

    much more likely to be rough. It is reported that when old sea ice becomes

    sufficiently modified so that it approaches the composition of fresh-water ice,

    it too will exhibit a tendency to candle.

            From Soviet data, young sea ice requires about 1 2/3 times the thickness

    of old sea ice to carry the same load, but this rule is very generalized. Lake

    ice is usually assumed to be 2 to 3 times stronger than sea ice, although its

    brittleness does not permit it to stand as much bending without cracking. River

    007      |      Vol_IIA-0346                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice.

    ice is generally not quite as strong as lake ice.

            Any entrapped matter such as silt, clay, or plankton (2) tends to weaken

    ice in the warmer periods because it absorbs sunlight and tends to cause

    internal melting because of the heat produced thereby.

            Ice containing much entrapped air tends to be weaker than clear essentially

    air-free ice. Tests by the Soils, Foundations and Frost Effects Laboratory

    of the New England Division, Corps of Engineers, in 1946-47, on 6 by 6 by [ ?]

    18-inch beams of artificial ice showed about 12% reduction in flexural strength

    on beams cut from cloudy ice manufactured from ordinary tap water, as compared

    with beams cut from clear air-free ice. Tests were performed at 10 ° to

    13° F.

            Effects of Horizontal Stratification in Ice . The strength of ice may be

    affected by development of horizontal laminae of variable properties. Variations

    in temperature, temporary thaws, rains, formation of snow-ice, flooding, and

    driving by the wind of salt spray onto the surface of otherwise relatively

    fresh ice or snow will all form horizontal layers in the ice sheet, the effect

    of which may be important in relatively thin ice but will be insignificant in

    heavy ice.

            Another stratification development occurs in coastal areas where river

    and stream inflows and tidal effects cause variations in the salinity of the

    water during the ice formation period. An influx [ ?] of relatively fresh water

    under the ice surface will result in rapid freezing to this surface, which may

    have cooled to as low as 28.6° F. when normal salt water was present under the

    ice. The same effect occurs in the polar seas during the summer thaw periods

    008      |      Vol_IIA-0347                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice.

    when meltwater from the surface sinks down through holes and freezes onto the

    cold undersurface of the ice pack. Such stratification in the lower part of

    the ice sheet, where critical tensile stresses occur when the ice is loaded,

    may be expected to have far greater effect on the over-all bearing capacity

    than laminations which develop in the upper half of the sheet.

            In the polar ice pack much less regular horizontal structure layering

    occurs when pressure causes rafting and buckling of the ice sheet.

            Effect of Vertical Cracks . Cracking of the ice sheet under the effect of

    temperature stresses results in a pattern of vertical defects or discontinuities

    distributed over the ice sheet. These do not ordinarily extend more than part .

    way through the depth of the ice. Although they are conspicuous in the upper

    surface of the sheet at low temperatures and may be readily visualized as a

    possible cause of weakness, static-load tests by the Soils, Foundations and

    Frost Effects Laboratory, in 1947, registered essentially no observable effect

    of such cracks on the bearing capacity or failure action of the ice under a

    load. Cracks formed due to the load showed very little tendency to follow the

    existing partial cracks. However, these tests involved only single-load

    applications, and it is reported that under heavy traffic, temperature cracks

    do have an effect to reduce the load-bearing capacity of the ice sheet.

    Cracks that pass all the way through the ice sheet seriously lower the load

    capacity and are especially hazardous if they occur under a snow blanket, as

    the snow may delay their refreezing and hide them from view.

            Temperature during Ice Formation . When ice forms very rapidly at extremely

    low temperatures there is less opportunity for dispersion of the impurities

    009      |      Vol_IIA-0348                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice.

    which are rejected by the ice crystals. Young sea ice formed at 14° F. has

    entrapped about 5 parts per 1,000 salt, but that formed at −40° F. has 10 to

    15 parts per 1,000. Differences in structure (and consequently of strength)

    of the ice would be expected to result from such differences in actual volume

    of included matter and the manner of its inclusion. It may be noted that the

    more concentrated brine surrounding the freezing crystals during fast freezing

    would tend to cause formation of the individual ice crystals at still lower

    temperatures than in ordinary sea water, with possible effects upon the ice

    properties.

            Residual Stresses . Internal stresses in ice specimens due to unadjusted

    temperature effects, to stresses introduced i [ ?] obtaining and preparing test

    specimens, or to external loadings of the ice sheet may well be in part re–

    sponsible for variability of reported test results.

            Effect of Temperature during Test . Temperature has a very pronounced

    effect upon the strength properties of ice, as shown in Table II.



    010      |      Vol_IIA-0349                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice.

    Table II. Effect of Temperature on Strength of Fresh-Water Ice.
    Temperature

    of

    test, °F.
    Strength tests, p.s.i. Direction of load–

    ing in relation to

    crystal optic axes
    Remarks Source
    Compres–

    sion
    Flexure Shear
    28 300 Perpendicular 3” to 5” square speci

    mens of St. Lawrence Ri–

    ver ice 5″ high; strees

    increased at approximate

    rates of 20 to 60 p.s.i./

    sec.
    (7)
    14 693
    2 797
    Tests with load applied

    parallel to crystal

    axes have been deleted
    28-30 156 Perpendicular 3″ wide × 2″ deep beams

    of St. Lawrence River ice,

    41″ span; loads applied

    at 14″ from supports;

    stress increased in in–

    crements at various

    rates averaging be–

    tween 0.175 and 1.4

    p.s.i./sec.
    (7)
    14-16 240
    28-30 184 Parallel ( a )
    14-16 214
    25 196 Essentially

    parallel ( a ) , ( b )
    6″ × 6″ beams of air–

    free artificial ice,

    18″ span; third point

    loading; stress in–

    creased at constant

    rates between 1.9 and

    2.6 p.s.i./sec.
    Soils, Fdns.

    & Frost

    Effects Lab.
    13 203
    −8 214

    ( a ) Where applied load is noted as acting parallel to optic axes, in flexure tests, bending stresses

    developed in beams act perpendicular to optic axes. ( b ) Some cur v ature of crystal structure existed because ice was frozen in containers from outside toward

    center, but this was minimized so far as possible in cutting out the test beams.

    011      |      Vol_IIA-0350                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice.

    Table II. Effect of Temperature on Strength of Fresh-Water Ice. ( contd. )
    Temperature

    of

    test, °F.
    Strength tests, p.s.i. Direction of load–

    ing in relation to

    crystal optic axes
    Remarks Source
    Compres–

    sion
    Flexure Shear
    32 180 94 Parallel ( a ) Artificial ice flexure

    specimens 2½″ to 6″ deep,

    2½″ to 5″ wide, 15″ to

    30″ long; shear specimens

    2½″ sq. and 6″ long;

    specimens failed in one

    to three minutes
    (15)
    2 - 90
    −9 256 -
    −10 - 115
    23 220 Parallel (nor–

    mal to the

    natural ice

    surface)
    5 cm. cubes of fresh –

    water ice; lower platten

    moved at constant rate

    of 0.1 mm./sec.; yield

    of upper load-measuring

    platten unknown
    (12)
    14 252
    5 354
    −4 394
    −13 488
    −22 506
    −31 584
    −40 615
    −49 665
    −58 694
    −67 725
    −76 779

    ( a ) Where applied load is noted as acting parallel to optic axes, in flexure tests, bending stresses developed in beams act perpendicular to optic axes.

    012      |      Vol_IIA-0351                                                                                                                  
    EA-I. Hansen-Linnel: Fresh & Salt Water Ice

            Vitman and Shandrikov conclude from their test results, shown in Table II,

    that the average compressive strength of ice increases more than four times

    as the temperature decreases to −76° F. (12) . The data on change of flexural

    strength with temperature also shows an increase with drop in temperature,

    though not as rapid as for compressive strength. Finlayson (5) found that

    temperature has very little if any effect on the strength of ice in shear,

    which is in agreement with the results of Horeth and Wilson (15) given in

    Table II. Under a given rate of increase of stress, the rate of deformation

    of the specimen rises (while the ultimate strength drops) with an increase

    in ice temperature; thus, ice, acting like a highly viscous material, flows

    more readily at higher temperatures.

            Effect of Rate of Loading on Strength Tests . Tests of ice specimens will

    give different results depending on the rate at which the load is applied.

    Numerous investigators have observed that ice will deform gradually under

    a steady load. However, there appears to have been only little practical

    investigation to determine the proper rates of load application for use in

    correlating test values with the load-supporting capacity of ice.

            From flexure tests reported by Brown in 1926, it was concluded that the

    modulus of rupture did not vary much at the different loading rates (7).

    However, when his results at 14 to 16° F. are plotted together with a number

    of flexure tests at 10° F. performed by the Soils, Fdoundations and Frost

    Effects Laboratory in 1946-47, covering a wider range of rates of loading,

    up to 7.65 p.s.i. per second, there is shown an apparent marked loss in

    ultimate strength with increase in the rate of application of stress. It

    is reasoned that if the indicated trend should be correct, then possibly the

    013      |      Vol_IIA-0352                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

    lower rates of stress increase permit plastic flow to occur at points [ ?] of

    initial stress concentration, thus allowing adjustment of stress distribution

    and higher breaking loads. It must be expected that the critical range

    of loading rates, over which maximum changes of results occur due to varying

    degrees of stress adjustment within the specimen, will be strongly dependent

    on temperature. Finlayson found in shear tests on ice, that at temperatures

    below 0° F., greater values were obtained when the load was applied rapidly (5).

            Effect of Orientation of Test Specimen . Since the bending stresses, which

    act in an ice sheet under load and which control in part the bearing capacity

    of the ice (the other factor being buoyancy), act in a direction parallel

    to the ice surface, analyses of bearing capacity should, theoretically at

    least, depend on tests in which specimens are stressed with their crystal

    axes oriented correspondingly. Practically, this offers difficulties,

    and if the bearing capacity of thick ice is to be determined from tests on

    cores recovered from borings into the ice, it will probably be necessary to

    establish an empirical relationship between strengths parallel to and at

    right angles to the surface of the ice sheet.

            Size and Proportions of Test Specimens . As in testing concrete or

    soils, the size and proportions of test specimens may be expected to influence

    the results of tests on ice. Certainly a test on a small portion of a single

    “needle” would not give the same results as a test on a collection of full–

    length , “needles.” What the minimum desirable size of specimen should be

    would be expected to vary with the type and condition of ice. However, there

    seems to have been little productive study given to this phase of ice testing

    as yet.



    014      |      Vol_IIA-0353                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

           

    Load-Bearing Capacity of Ice

            Records of Actual Ice Loadings . Records of the innumerable, and in

    many areas regular, actual ice crossings which have been made with motor

    vehicles, tractors, sleds, railroad trains, etc., appear to be a rather

    meager source of data on the supporting capacity of ice for several reasons.

    First, when such crossings have been made, there appears to have been only

    rarely any attempt to record the actual conditions of the crossing, such as

    ice thickness and quality, weight of machine, temperature, size and shape

    of loaded area, and presence of snow cover. Second, when such observations

    have been made, they have been incomplete since all the factors involved

    may not have been recognized. Third, there seems to have been little

    interest in making such records generally available in publications.

    Empirical rules have been developed on the basis of experience with crossings,

    but it is difficult to trace these back to original records.

            Historical Military Rules . There are a number of old rules relating to

    the load-bearing capacity of ice which mostly have their origin in military

    engineering and are the result of observation and experience in the movement

    of troops, equipment, and supplies across frozen bodies of fresh water.

    The data in Table III are a modernized and improved version of these rules

    (11). The rules should be considered to apply to fresh - water ice of good

    color and soundness, away from unsupported edges. The thickness measure–

    ments should disregard any soft or poor quality ice on the top or bottom

    of the ice sheet.



    015      |      Vol_IIA-0354                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

    Table III. Load Capacity of Ice.
    Load Thickness

    of ice, in.
    Minimum

    interval,

    ft.
    Single rifleman on skis or snowshoes 1.5 16
    Infantry in single file, 2-pace distance ( a ) 3 23
    Infantry columns , ( a ) , single horses, motorcycles,

    unloaded sleds, or motor toboggans
    4 33
    Single light artillery place, ¼-ton truck, 4 × 4 6 49
    Light artillery, passenger cars, medium 1½-ton

    trucks with total load of 3½ tons
    8 65
    2½-ton trucks, light loads 10 82
    Closed columns of all arms except armored force

    and heavy artillery ( a )
    12 98
    Armored scout cars, light tanks 14 115
    20-ton vehicles 16 131
    45-ton vehicles 24 164

    ( a ) Minimum intervals shown are distances between files.

            Moskatov’s Empirical Method . Moskatov (10) has given a procedure for

    determining required ice thicknesses for aircraft on skis which he calls the

    “Method of Analogy.” Formulas derived by this method are given in Table IV.

    The basic formulas for aircraft on skis have been adapted to the case of

    wheels by use of a factor of 20%, which is used by the Russians. P is the

    gross weight of aircraft in tons and t is the ice thickness in inches. The

    016      |      Vol_IIA-0355                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

    formulas are said to apply only for ice formed and maintained at a tempera–

    ture below 16° F. At higher temperatures 25% greater thickness is required.

    Table IV. Minimum Required Ice Thickness in Inches.
    Type of ice Aircraft on skis Aircraft on wheels
    Lake ice t = (27/8)√(P) t = (81/20)√(P)
    River ice t = (15/4)√(P) t = (9/2)√(P)
    Old sea ice t = (27/4)√(P) t = (81/10)√(P)
    Young sea ice t = (81/8)√(P) t = (243/20)√(P)

            The formulas given in Table IV are simple and they indicate that the

    carrying capacity of the ice varies as the square of the ice thickness;

    this is confirmed approximately by elastic theory analysis. Design curves

    from these formulas are shown on Figures 1 and 2, where they are designated

    as “Russian (Moskatov) Empirical Analysis.”

            Elastic Theory Analysis . If a stationary load is placed upon the surface

    of a floating ice sheet which extends out to a large distance on all sides

    from the load, a deformation of the ice sheet occurs which is a maximum under

    the loaded area and which extends outward in all directions, decreasing in

    amplitude with distance from the center. When the deformation occurs, a

    buoyancy force is caused to act upward on the bottom of the ice sheet. This

    force is at any point directly proportional to the deflection at that p o int

    as long as the ice does not become submerged, with water flooding on top.

    016a      |      Vol_IIA-0356                                                                                                                  

    Fig. 1.

    BEARING CAPACITY OF OLD SEA ICE

    FOR

    AIRPLANES WITH WHEELS

    JANUARY-1949



    016b      |      Vol_IIA-0357                                                                                                                  

    Fig. 2.

    BEARING CAPACITY OF

    FRESH-WATER ICE FOR

    AIRPLANES WITH WHEELS

    JANUARY-1949



    017      |      Vol_IIA-0358                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

    At the same time, the bending strength within the ice sheet itself is

    mobilized. The buoyancy and bending resistance forces combine to provide

    the total supporting force for the applied load. (When, as may occur along

    a shore line, the water drops away from under the ice leaving it suspended,

    the ice sheet will have at that location greatly reduced load-supporting

    capacity.)

            Since under static loading the buoyant force of the underlying water

    at any point acts in exact proportion to the amount of deflection of the ice

    sheet at that point, the latter may be assumed to have a perfectly elastic

    support. If we may also assume that the ice sheet has properties approximating

    those of an elastic slab, then the theories of elasticity may be applied to

    compute stresses and deformations in the ice sheet and to determine thicknesses

    required for given conditions of loading.

            As pointed out by Volkov, static loading of floating ice is more critical

    than impact loading. Under an impact force, the ice is simply compressed

    between the applied load [ ?] [ ?] and the underlying water; in order to develop

    bending stresses, a definite volume of water must be displaced from under the

    ice, near the area of load application, and under a sharply applied load the

    time required for this movement to occur is insufficient. Shearing action

    is usually not critical. Experience has shown that thin ice may be crossed

    by a moving load when a stationary load would break through and also that

    thin ice may sustain a stationary load for some time, then give away. Thus,

    load-capacity studies may be based upon the static loading condition, except

    as it may be necessary to apply modifications for wave action under moving

    loads and for fatigue under repeated loadings.



    018      |      Vol_IIA-0359                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

            For the condition of static loading, a comprehensive theoretical

    analysis of the bearing capacity of floating ice has been developed by

    Mr. H. F. Shea of the Soils, Foundations and Frost Effects Laboratory by

    adapting to the case of an ice sheet formulas developed by Dr. H. M. Wester–

    gaard for determining the stresses at the interior portion of an elastically

    supported slab (14). In their general form, the formulas are not adapted

    to giving quick answers since results must be computed. However, the

    formulas permit analysis of a variety of combinations of loading patterns

    and intensities which could not otherwise be approached.

            For uniformly loaded circular areas, these formulas are as follows:

            (1) Inside the area of loading:

    fx and fy = (0.6517P/t2)[1.6713 + (3/4) loget – logeB + (0.012B2/t3/2)] + (0.1516P/t2)[(r2/450B2)(cos2Θ)]



    019      |      Vol_IIA-0360                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

            (2) Outside the area of loading:

            fx and fy = (0.6517P/t2)[1.6713 + (3/4) loget – logeB + (0.012B2/t3/2)] + (0.1516P/t2)[(r2/450B2)(cos2Θ)] )] c = √(1.6d2 + t2) – 0.675t when d < 1.724t c = d when d > 1.724t

            For uniformly loaded elliptical areas (or where a uniformly loaded

    ellpitical area may be reasonably assumed), the following stress equations

    apply:

            (1) Inside the area:

            fx and fy = (0.6517P/t2)[5.0372 + (3/4) loget – loge (a + b) – x2/(a(a + b)) – y2/(b(a + b))] ± (0.1516P/t2)[((ba)/(a + b)) – (2ab/(a + b2)) ((x2/a2) – (y2/b2))]



    020      |      Vol_IIA-0361                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

            (2) Outside the ellipse, for, y = o, x = a ,

            fx and fy = (0.6517P/t2)[5.0372 + (3/4) loget – loge (x + √(x2 - a2 b2)) – x/(x + √(x2a2 [suspect missing symbol here] b2)] ± (0.1516P/t2) [((a2 + b2)/(b2a2)) – 4b2x/((b2a2) (x + √(x2 + a2b2)]

            (3) Outside the ellipse, for, x = o, y = b ,

            fx and fy = (0.6517P/t2)[5.0372 + (3/4) loget – loge (y + √(y2 + a2 - b2)) – y/(y + √(y2 + a2b2))] ± (0.1516P/t2) [((a2 + b2)/(b2a2) – 4a2y/((b2a2) (y + √(y2 + a2b2))]



    021      |      Vol_IIA-0362                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

            In these formulas the notation is as follows:

            f x , f y = bending stresses in p.s.i. at surface of ice at points

    x , y on coordinate axes

            P = total applied load in pounds

            t = thickness of ice in inches

            e = base of natural logarithms = 2.7128

            B = ratio of radius of circular area to radius of standard

    bearing plate (15 inches) = c/15

            r = radial distance from center of circular area to point

    of stress investigation in inches .

            θ = angle between x axis and line drawn between point of

    stress investigation and center of circle

            a = minor radius of elliptical area in inches

            b = major radius of elliptical area in inches

            c = substitute radius of loaded area in inches

            d = actual radius of loaded area in inches

            a and b are further identified by the equation for an ellipse, (x2/a2) + (y2/b2) = 1

            For example, the stresses induced by a 60,000-1b. load transmitted

    to ice 50 in. thick by a B-29 main dual wheel unit, assuming load is dis–

    tributed equally over two circular areas, was determined.

            ( 1 ) Given the following data:

            Area (for one circular area) = 370 sq.in.

            Radius of circle, d = 10.9 in.

            Distance between wheel centers = 37.3 in.

            c = √(1.6d2 + t2) – 0.675t P = 30,000 lb. t = 50 in.

            P = 30,000 lb.

            t = 50 in.



    022      |      Vol_IIA-0363                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

            (2) Using formulas (1) and (2) for the case of the circular areas:

            f = 37 p.s.i. when x = 0 and y = 0

            f = 26 p.s.i. when x = 37 p.s.i. and y = 0

            total f = 37 + 26 = 63 p.s.i.

            In the above formulas, the following constants were assumed:

            Poisson’s ratio for ice = 0.365

            Modulus of elasticity = 1,294,000 p.s.i.

            Observed values of Poisson’s ratio are reported variously from 0.25 to [ 0138 ?]

    0.38 and the value adopted above for the computations is, therefore, near the

    higher limit. Stress-strain moduli have been reported by various investigators

    from under 70,000 to over 1,500,000 p.s.i. Recent flexure tests by the Soils,

    Foundation and Frost Effects Laboratory showed a tangent modulus value of

    610,000 p.s.i. on a single specimen of artificial ice at 10° F. up to a

    strees of about 25 p.s.i.; near the ultimate failure stress of 212 p.s.i., the

    secant modulus (related to the origin of the stress-strain curve) was approxi–

    mately 190,000 p.s.i. A value of approximately 400,000 p.s.i. was also

    determined from the deflection of a naturally formed fresh - water ice sheet

    8.4 in. thick in a 27-ft. tank when loaded at approximately 10° F. Brown has

    also presented considerable data on effects of temperature, and of rate and

    range of loading, on stress-strain moduli (7), which indicate generally lower

    values than the one adopted above for computation of the equations. Reduction

    of assumed value for either Poisson’s ratio or modulus of elasticity in the

    equations will result in an indicated increase in load capacity. Thus, the

    formulas, as given above, are on the conservative side with respect to these

    basic values.



    023      |      Vol_IIA-0364                                                                                                                  
    EA-I. Hansen-Linell; Fresh & Salt Water Ice

            Once the thickness of ice required for a given load, size of area, and

    factor of safety has been determined, the thickness required for a different

    load on the same loaded area and with the same factor of safety may be

    computed from the relation that the thickness required varies directly with

    the square root of the load.

            Preliminary Elastic Theory Ice Thickness Curves . Curves derived from

    the elastic theory equations as presented are shown on Figures 1 and 2 for

    aircraft with wheels and designated thereon by the phrase “Elastic Theory

    Analysis.”

            The curves of Figures 1 and 2 have been computed with the following ice

    strengths, assumed as conservative values for ice under the temperature condi–

    tions noted on the figures:

            Hard, sound lake ice = 150 p.s.i.

            Hard, sound river ice = 125 p.s.i.

            Old sea ice (more than 1 year old) = 75 p.s.i.

            Similar curves could be computed for other types of loadings, such as for

    tractors, sleds, aircraft with skis, and even structure footings. Figures 1

    and 2 show results of a few actual loadings by planes and in tests.

            Comments on Elastic Theory Method and Thickness Curves . Although as yet

    not complete k ly proved, the elastic theory equations which have been given

    are considered the most accurate theoretical approach available. The constants

    used in the equations are subject to considerable modification as more is

    learned about the properties of ice. It may be that eventually more than one

    set of constants will have to be used.



    024      |      Vol_IIA-0365                                                                                                                  
    EA I. Hansen-Linell: Fresh & Salt Water Ice

            For theoretical analysis purposes, the ice sheet has conventionally been

    assumed to be in equilibrium under external forces and unstressed. This is

    likely to be far from the truth in the upper part of the slab. The stress

    pattern in the upper part of an unloaded ice sheet due to temperature and

    lateral forces must be very complex. That the stresses may be high is shown

    by the cracking which occurs due to temperature alone. Fortunately, however,

    elastic theory analysis shows that under an applied vertical load, the critical

    stresses act in the lower portion of the slab where temperature stresses

    are at a minimum.

            It should be emphasized that the curves apply at the interior of an ice

    sheet; near the edge of a crack or open water, the load-supporting capacity

    can be expected to be much less.

            It is also emphasized that the curves plotted on Figures 1 and 2 from the

    elastic theory are preliminary, and are necessarily over-simplified. It is

    obviously not possible to [ ?] adopt one strength value for fresh - water ice

    and one for salt - water ice and expect that all ice in all latitudes and

    locations will conform to either one or the other of those standards under

    all the wide variety of conditions of salinity, temperature, and other factors

    which will be encountered. Rather, the curves are guides to the approximate

    answer, based on conservative strength assumptions. From the small experience

    acquired to date, it is believed that the curves for factor of safety of 2.0

    represent very safe thickness values under the limitations stated on the

    curve sheets. Below the latter curves is a “zone of uncertainty,” extending to

    below the curves from the Russian (Moskatov) Empirical Analysis. It is this

    025      |      Vol_IIA-0366                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

    zone of uncertainty which future studies of the bearing capacity of ice

    sheets should explore. Eventually, there will probably be not just two but

    a considerable number of curve sheets to cover the many possible combinations

    of ice strength, temperature, salinity, and other variables. With such curves

    and with the results of quick field tests of the characteristics of the ice

    in question, using test apparatus of types now beginning to be developed,

    accurate numerical evaluations of the load-bearing capacity of ice should

    be possible. However, for the present, prudent procedure in critical cases

    is to weigh together the empirical rules and formulas, the elastic theory

    equations, and the promptings of judgment and experience.

            Effects of Moving Loads . Russian investigators have observed the

    possibility of danger from development of resonance in waves created in the

    ice sheet under moving loads and have actually encountered conditions in which

    several machines in motion and passing each other in both directions set up

    such wave action that the ice broke (6). They have reported that such occur–

    rence becomes especially dangerous when the machines are traveling at speeds

    corresponding to those of the propagation of the ice waves and that in such

    a case a single vehicle can produce sufficiently strong resonant vibrations

    to cause it to break. The Russians have prepared rules for speed and spacing

    of vehicles to avoid this effect. On ice about 24 inches thick, over water

    of the order of 16 to 33 feet deep, the Russians have found that at speeds

    between 3 and 9 miles per hour a depression of the ice under the vehicle moves

    at the same speed as the vehicle. At speeds above about 12 miles per hour,

    wave vibrations are formed which spread far to the sides of the path, at speeds

    which on this lake were found to be 19 to 25 miles per hour. They concluded

    that on this lake initial speeds of about either 15 or 25 miles per hour should

    026      |      Vol_IIA-0367                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

    be maintained and that speeds intermediate between these rates should be

    avoided. Overtaking of one machine by another should also be avoided, and

    spacings between vehicles varying from 200 feet to 650 feet and more were

    recommended, depending on the speed of movement and the strength of the ice.

    Particular caution was advised near shores where complex wave effects may

    occur.

            Repetition of loading under extensive operations causes ice to become

    weakened. It is reported that one reason for this is the progressive

    deepening of temperature cracks under the flexing action of heavy traffic.

    Under such conditions, a desirable procedure is to provide sufficient area,

    or alternate routes, so as to permit frequent changes in traffic lanes.

            It is also reported that ice will break up much more readily under

    vehicles with low-speed motors than under those with high-speed motors,

    because of the differences in frequency and intensity of vibrations trans–

    mitted to the ice. Traveling parallel to major cracks must be avoided.

            Methods of Increasing Supporting Capacity of Ice. The bearing value of

    an ice sheet may be increased by: (1) thickening the ice sheet as a struc–

    tural member, and (2) distributing the load over a wider area of application.

            The ice thickness may be increased on the top by flooding the surface

    in shallow layers, allowing each to freeze completely before adding the

    following one, or the increase may be obtained naturally on the bottom of

    the ice layer, over a longer period, by either keeping snow cleared entirely

    from the surface or by packing the snow cover down solidly so as to increase

    the rate of heat loss from the underlying water and thereby speed freezing.

    Because even tightly compacted snow has insulating qualities, rate of thickening

    027      |      Vol_IIA-0368                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

    will be higher if snow is completely removed. If a heavy thickness of snow

    covers the ice, it may sometimes be possible to assist the flooding procedure

    by boring holes through the ice at intervals, the weight of the snow being

    sufficient to submerge the ice and saturate the snow. However, flooding of

    snow must carry through at least to the top of the snow cover, otherwise

    the insulating effect of the unwet upper zone of the snow will permit the

    underlying water-snow mixture to remain as slush for a long period without

    freezing.

            Although superficial wetting down and/or compaction of the snow cover

    sufficiently to produce a hard vehicle surface may result in a higher bearing

    capacity of the ice sheet, it is likely that this results mostly from the

    load distributing characteristics of the snow layer and the increase in ice

    thickness which develops from the increased thermal conductivity of the layer.

            The load may also be distributed over a wider area by means of brush,

    straw, plank, logs, or ice blocks laid on the ice, which may in turn be

    covered with a layer of compacted snow to provide smooth travel and possibly

    additional load distribution effect. Care must be taken to periodically

    check ice thickness when such procedures are used, as the ice may melt on its

    undersurface as layers are added on the upper surface, if the original ice

    thickness has been in balance with the existing temperature conditions, if

    the added materials have insulating qualities, or if currents are present.

            At the weak zone which exists where ice is not frozen to the shore, or

    at open cracks, adequate bearing capacity is usually best obtained by bridging

    over with timber or other structural materials (13).



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    EA-I. Hansen-Linell: Fresh & Salt Water Ice


    BIBLIOGRAPHY

    1. Barnes, H.T. Ice Engineering . Montreal, Renouf, 1928.

    2. Boorke, A. Morskie Ldy . (Sea Ice.) Moscow, Leningrad, Izdatelatvo

    Glavsevmorputi, 1940. Polar Workers Library . Translation by E.

    Olkhine in The Stefaneson Library, New York City.

    3. Dorsey, N.E., comp. Properties of Ordinary Water Substance . N.Y., Reinhold,

    1940. American Chemical Society. Monograph Series.

    4. Finlayson, J.N. “Icebergs as ships,” Engineer , Lond. June 7, 1946,

    pp.517-18.

    5. ----. “Tests on the shearing strength of ice,” Canad.Engr . vol.53, no.1,

    pp.101-103, July 5, 1927.

    6. Ivanov, K. Ye., Kobeko, P.P., and Shulman, A.R. Deformatsiia Ledovogo

    Pokrova pri Dvizhenii Gruzov . (Deformation of an Ice Cover under

    Moving Loads.) Leningrad, Akademiia Nauk, S.S.S.R., Fiziko–

    Tekhnicheskii Institutt, 25 July 1945.

    7. Joint Board of Engineers on St. Lawrence Waterway Project. Report...November

    16, 1926. Ottawa, Acland, 1927, Appendix F.

    8. Malmgren, Finn. On the Properties of Sea Ice . Bergen, Grieg, 1927. Maud

    Expedition, 1918-1925. Scientific Results , vol.1, no.5.

    9. McConnel, J.C. “On the plasticity of an ice crystal,” Roy.Soc.Lond., Proc .

    vol.49, pp. 323-43, Mar. 12, 1891.

    10. Moskatov, K.A. “On posadke samoletov na led.” (Airplane landings on ice.)

    Leningrad. Arktichaskii Nauchnyi-Issled.Inst. Trudy . T.110, pt.1,

    art.5, pp.43-55. In Russian with English summary. Translated and

    edited by Headquarters, U.S. Air Forces.

    11. U.S. War Department. Operations in Snow and Extreme Cold . Wash.,D.C.,

    G.P.O., 1944. Basic Field Manual FM 70-15.

    12. Vitman, F.F., and Shandrikov, N. P . “Nekotorye issledovaniia mekhanicheskoi

    prochnosti lda.” (A study of the mechanical strength of ice.)

    Leningrad. Arkticheskii Nauchnyi-Issled.Inst. Trudy , T.110, pt.1,

    art.7, pp.83-100. Translated and edited by Headquarters, U.S. Air

    Forces.

    13. Westergaard, H.M. Expedient Snow and Ice Roads . Wash.,D.C., G.P.O.,

    26 September 1944. U.S. Army. Technical Bulletin TB Eng . 42.



    029      |      Vol_IIA-0370                                                                                                                  
    EA-I. Hansen-Linell: Fresh & Salt Water Ice

    14. ----. “Stress concentrations in plates loaded over small areas,”

    Amer.Soc.Civ.Engrs. Trans . vol.69, no.8, pt.2, pp.831-86, 1943.

    15. Wilson, J.T., and Horeth, J.M. “Bending and shear tests on lake ice,”

    Amer.Geophys.Un. Trans . vol.29, no.6, pp.909-12, Dec., 1948.

           

    Ralph Hansen and Kenneth Linell



    Unpaginated      |      Vol_IIA-0371                                                                                                                  

    Construction and Maintenance of Airfields in the Far North Regions

    EA-I: (James D. Lang)

    CONSTRUCTION AND MAINTENANCE OF AIRFIELDS

    IN THE FAR NORTH REGIONS

           

    CONTENTS

    Page
    Introduction 1
    Types of Airfields 3
    Reconnaissance 6
    Planning and Design 8
    Construction 12
    Grading 17
    Preparation of the Subgrade 18
    Paving 20
    Snow Removal and Maintenance 20



    001      |      Vol_IIA-0372                                                                                                                  
    [EA-I: James D. Lang]

           

    CONSTRUCTION AND MAINTENANCE OF AIRFIELDS

    IN THE FAR NORTH REGIONS

           

    INTRODUCTION

            The engineering aspects of the subjects of airfields, pavements, roads,

    and drainage as they apply to the arctic and subarctic regions readily lend

    themselves to treatment as a single discussion. While the actual construction

    of these items follows the usual pattern normally employed in more temperate

    regions, the engineering aspects do not. Seldom, if ever, does engineering

    play such an important part as it does in the Arctic in the conception and

    execution of any construction program. For airfield construction, in parti–

    cular, never is proper engineering as important as when such construction is

    contemplated for the Arctic.

            Assuming that for strategic, economic, navigational, or other reasons an

    airfield must be built in a given area, flying characteristics of the site will

    usually be the deciding factor in most areas of the world. In the Arctic, on

    the other hand, more frequently engineering factors determine which one of

    several sites will be chosen. Of course, both factors must be considered and

    the best possible compromise be chosen, consistent with the mission.



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    EA-I. Lang: Construction and Maintenance of Airfields

            Let us examine why engineering becomes so important. Arctic areas are

    remote, relatively inaccessible, and devoid of facilities with which to per–

    form any construction. The construction season is so short that any mistakes

    or omissions are disastrous and may well result in the probable loss of one

    full year in completion for each major error. The severity of the climate

    creates problems of cold, wind, fog, snow, ice, permafrost, ice fields, and

    other phenomena for which special measures must be taken. Any one or more of

    the above conditions creates a requirement for extreme care in selecting and

    examining sites and planning for the construction in minute detail. A firm

    mental picture must be had of each and every move before any steps are taken,

    otherwise valuable effort, time, and money will be lost, not only in determin–

    ing the next measure to be taken, but probably in undoing false steps which

    already may have been taken. Presolving problems and planning in detail so

    as to permit completion of arctic construction at a minimum of cost in time,

    [ ?] effort, and expense involves engineering of the highest caliber. It

    cannot be overemphasized that construction such as is discussed herein involves

    an engineering problem requiring the utmost skill in planning and execution

    and that it is best to make haste slowly.

            Elsewhere in this encyclopedia are discussions of various natural phenomena

    encountered in the Arctic. Before proceeding with this article it might be well

    for the reader to familiarize himself with the general subject of permafrost in

    order to understand what it is and how it behaves, also with the subjects of

    surface and subsurface drainage. The engineer in the Arctic cannot undertake

    any construction project involving excavation, drilling, pile driving, or even

    just disturbing the earth’s surface without encountering either frost or

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    EA-I. Lang: Construction & Maintenance of Airfields

    drainage problems. Briefly, permafrost is a condition of eternally frozen

    soil as distinct from eternally frozen icecaps and glaciers or from soil

    subject to seasonal frost. Permafrost is beneath the surface and may exist

    either as a continuous layer, or in lenses and pockets. How far the perma–

    frost table may be from the surface varies from a few inches to many feet and

    depends to a great extent upon the type of surface material above it, the

    classification of the soil, and the subsurface drainage pattern. The ground

    above the permafrost table is known as the active zone since it alternately

    freezes and thaws, however, not necessarily to the same degree each year.

    Ground water may exist below, within or above permafrost, and may be either

    under pressure or free flowing, depending upon whether there are nearby high

    elevations to provide the hydrostatic head or whether plains or areas of weak–

    ness exist to relieve the pressure. It is obvious that during thousands of

    years of direct exposure to extreme cold, nature has set up a balance, or

    thermal regime, which exists within narrow limits. Any disturbance or new

    outside influence will upset that regime. Construction activity provides the

    influence to disturb e or upset nature’s balance. It is the engineer s problem

    either to avoid disturbing the balance or to devise ways and means of diverting

    the disturbed condition to his own advantage.

           

    TYPES OF AIRFIELDS

            For military operations in the Arctic, three general types of airfields may

    be involved. These are ice fields, light airfields, and heavy airfields , . Ice

    fields, as the term implies, involves construction of a temporary nature and,

    of necessity, such construction is employed when hasty measures and rapid

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    EA-I. Lang: Construction & Maintenance of Airfields

    construction are required. In certain areas, of course, such as on an icecap,

    these are the only fields possible. The principal requirements of the ice

    field site selection are that the site must be able to support the mission for

    which the field is being built; that the site must possess adequate flying

    characteristics as to glide angles, wind direction, and grades; that the site

    must be logistically supportable for the unit expected to operate therefrom;

    that the terrain must be relatively level so as to minimize the amount of sub–

    grading preparation; and that adequate quantities of loose snow must be avail–

    able in order to provide surface materials for fine grading and compaction.

    If a site can be selected which generally meets the foregoing criteria, the

    problem of preparing the field becomes relatively simple. Methods of grading

    and compaction of snow and ice utilize standard construction equipment and

    techniques and present a problem quite similar to that encountered in grading

    and compacting silty soils. An important element in selection of an ice field,

    which has not heretofore been mentioned, is the selection of a site possessing

    a suitable alternate landing area such that it may be developed into a permanent

    field during the ensuing summer construction season should circumstances require

    that flight operations be maintained for a prolonged period of time from the

    general area. The ideal solution would be to select a location where this

    permanent airfield could be built to utilize such structures and base facilities

    as have been provided for the snow and ice field without the necessity of

    extensive relocation of facilities or travel of unnecessary great distances

    between the permanent airfield site and the base facilities.

            The second type of airfield, the light airfield, is one which again must

    be selected and constructed usually in a minimum of time. This type of field

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    EA-I. Lang: Construction & Maintenance of Airfields

    involves the element of site selection to meet the requirements of mission,

    flight characteristics, and logistic support. It also must meet the require–

    men e t of enabling rapid construction of a base which can be used for year-round

    operations. In general, the construction of a light airfield involves the

    selection of a suitable flight area on which an airfield may be constructed,

    utilizing nearby aggregate sources of free draining material, and spreading

    and compacting these materials upon the undisturbed natur e al surface of the

    ground in such a manner as to avoid cuts. This type of field requires rela–

    tively short and narrow runways, and can be completed with conventional methods

    and equipment with little added difficulty over that which could be expected in

    a more temperate climate.

            The third type of airfield, and the one which presents the greatest prob–

    lem, is the heavy airfield. This installation requires a great deal of [ ?]

    equipment, time, and effort and should be built only after the greatest delibera–

    tion and consideration of all factors involved. The site selected must, of

    course, meet the requirements of the mission to be performed and the flight

    characteristics of the aircraft to be employed therefrom. These criteria

    are of secondary importance, however, to possession of desirable engineering

    characteristics. This is not to say that the mission and flight characteristics

    can be neglected, but it is intended to mean that fields of lesser desirability

    from the standpoint of these two characteristics may be selected if the

    engineering character i s tics are otherwise more advantageous.

            Selection of any of the three types of fields discussed above naturally

    rests upon proper reconnaissance of all available sites within the general

    area from which the mission can be performed.



    006      |      Vol_IIA-0377                                                                                                                  
    EA-I. L o a ng: Construction & Maintenance of Airfields

           

    RECONNAISSANCE

            The initial airfield reconnaissance can best be performed by air.

    However, prior to such a move, a careful map study should be made to select

    the general areas from which the mission can be performed and to eliminate

    from those areas specific regions where mountainous terrain, lakes, sinuous

    rivers, or other geographic factors obviously preclude consideration. A

    systematic flight pattern should be set up and a suitable slow-flying

    aircraft having good facilities for observation of the ground should be

    employed. Experience in arctic areas has proved that observation of surface

    condition will provide several excellent clues to the nature of subsurface

    conditions which may be encountered. Areas covered by hummocky tundra, commonly

    known as “nigger heads,” indicate the existence of a permafrost table near

    the surface, poor drainage, and a general water-logged condition. This condi–

    tion is true even where the existence of plateaus with sharply defined hill–

    sides or terraces would otherwise indicate that there should be adequate

    drainage from the area. The existence of a growth of birch trees indicates

    thawed ground, i.e., an area which does not freeze between the permafrost and

    the surface active zone. The existence of spruce trees indicates a permafrost

    table relatively near the surface of the ground and poor drainage. On the

    other hand, the occurrence of pine and fir trees indicates a well-drained

    granular soil which in turn means that water flowing through this pervious

    layer will have had a tendency to melt and lower the permafrost table. Such

    sites are worthy of close investigation by ground parties and are indicative

    of the most feasible airfield site. Areas covered by willows generally are

    unsuitable since willows indicate the existence of ground water and a site

    007      |      Vol_IIA-0378                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

    likely to be troubled with surface ice during the winter months. Areas covered

    by tree growth, which is irregular, and containing individual trees inclined

    at odd angles indicate ground susceptible to swelling and frost mounds. Areas

    devoid of trees and shrubs and which are covered by tundra and moss indicate

    a high permafrost table, particularly such areas that have a “crackled” appear–

    ance [ ?] or the octagonal designs characteristic of a high permafrost table.

    Exposures of rock outcroppings indicate areas where the seepage of water

    in the planes next to the rock is apt to cause a melting of the permafrost

    and the development of subsurface channels of flowing water, which may make

    construction exceedingly troublesome.

            Having selected a number of possible sites from the air, arrangements

    should be made for further investigation of [ ?] these areas by ground

    parties. Preferably a base of operations should be selected for the ground

    parties from which several of the sites may readily be investigated. The ground

    parties should consist of individuals who are experienced in the Arctic.

    Parties should be equipped with normal survey instruments for complete and

    detailed topographic surveys of the sites in question, also with light drilling

    equipment and excavation tools for the digging of numerous test holes and

    test pits, and also meteorologic equipment to initiate weather observations

    throughout the entire period the party is in the area. It is extremely impor–

    tant that a large number of test holes and test pits be dug to determine the

    depth of the permafrost table; the characteristics of subsurface soils; the

    existence, depth, temperature, volume, and direction of the flow of water; and

    the nature of the natural insulating material which is found on the surface.

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    EA-I. Lang: Construction & Maintenance of Airfields

    Detailed notations should be made of all natural phenomena, carefully logged

    and plotted on an area sketch. Test holes and test pits should be care–

    fully back-filled with material as nearly similar to the original material

    in order to avoid disturbance of natural conditions. It is important that

    insulating materials be left on the surface so as not to induce subsequent

    thawing in the area investigated. When conditions are encountered which

    indicate the unsuitability of a given site for airfield construction, a care–

    ful verification should be made and then further efforts suspended on that

    particular site in order to conserve time for additional observations and

    tests at other sites which have not been definitely eliminated. At best, the

    time available for reconnaissance is limited so that as rapidly as site

    selection can be narrowed to one particular location it should be done in

    order that the maximum information may be developed on the final site prior

    to committing the construction forces.

           

    PLANNING AND DESIGN

            Following selection of a site, planning the construction operation must

    be thoroughly, completely, and exhaustively pursued. Every scrap of engineer–

    ing data accumulated during the reconnaissance must be reanalyzed and evaluated.

    Maps, sketches, geological and geophysical reports, verbal reports, photographs,

    long-range weather observations, ice tables, communication routes, available

    equipment (both qualitatively and quantitatively), manning tables, shipping

    capabilities, and the available time must be carefully reviewed until a firm

    visualization of the construction problem is grasped with confidence. The

    planner must then carefully fit these bits and pieces together, matching his

    009      |      Vol_IIA-0380                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

    capabilities against his minimum requirements. One of the major considerations

    he must face is the provision of adequate living accommodations and opera–

    tional facilities for the construction force. Construction of these items

    is a major operation in itself and is a heavy drain on manpower and resources.

    It follows that not one square foot of building construction should be pro–

    vided, which is not absolutely necessary, and not one man should be permitted

    on the construction site who is not fully qualified in his field and whose

    full-time presence is not needed. No equipment should be brought to the site

    unless the exact need for that equipment is anticipated beforehand.

            A second major consideration to be given during the planning phase is

    that of establishing minimum requirements. It is a constant temptation to

    add to the scope of any project. The planner must resist these tendencies

    and enlist every means at his disposal to minimize and simplify his problem.

    It is better to complete a spart o a n-like installation on time than it is to

    half complete an ideal plan. Time, manpower, and mat e é riel devoted to a non–

    essential may mean failure to complete one element of the over-all project;

    such failure might mean the loss of an entire year in obtaining final use of

    the installation.

            To return to some of the engineering aspects of the planning, it is

    essential that standard plans be selected or engineering designs be prepared

    in advance of construction operations. This is where the data accumulated

    during the reconnaissance and study phase of the project can be invaluable.

    The drainage pattern, both surface and subsurface, is the key to the design

    of the airfield. The landing strip, taxiways, parking aprons, and roads must

    010      |      Vol_IIA-0381                                                                                                                  
    EA-I. Lang: Construction a Maintenance of Airfields

    be located and designed so as to create the least possible disturbance to

    the natural drainage pattern. Where disturbance cannot be avoided, then a

    solution must be adopted which will take advantage of, rather than attempt

    to defy, the natural arctic phenomena known to exist. Deep and narrow drain–

    age ditches must be planned to by-pass and reroute surface drainage from

    construction areas. Subsurface patterns must be broken at critical points

    several hundred feet away by providing deep ditches to be cut into the perma–

    frost so as to create planes of weakness which will rupture and permit sub–

    surface drainage either to be diverted away from the building areas or im–

    pounded in induced ponds or ice fields away from the critical areas. Plans

    should contemplate that natural insulating materials be left intact wherever

    possible or be restored using similar natural materials stripped from other

    areas remote from the airfield when disturbance cannot be avoided. The

    grades, both longitudinal and latitudinal, of the runways and its appurtenances

    should be set such that fills and not cuts are required in establishing final

    surfaces.

            The building area for camp structures should be located downhill from

    the landing field. Downhill, in this instance, is in terms of subsurface

    drainage and not necessarily in terms of surface elevations. Construction

    operation buildings, such as shops and warehouses, should be located between

    the airfield and the camp. All structures should be located a minimum of one–

    fourth mile away from the airfield, and preferably farther, up to one mile.

    These distances are desirable to provide room for ex ap pa nsion, to minimize the

    effects on the runway of ice fog that will form in the vicinity of the heated

    structures at temperatures below approximately minus 40 degrees Fahrenheit,

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    and to minimize the effect on the subsurface drainage pattern both from the

    standpoint of the effect of the airfield drainage pattern upon the building

    area and vice versa. Structures themselves should be designed to minimize

    shipping space required and to utilize local materials where possible. It

    also is highly advisable to utilize prefabricated or precut designs to

    minimize the manpower required at the site for erection.

            The design of the airfield landing strips, taxiways, aprons, and road

    system will depend upon the type and nature of the aircraft and vehicles

    which may be expected to operate upon them. It is beyond the scope of this

    discussion to deal with the technical aspects of how this design is done, but

    it is sufficient to note that standard engineering practice is followed to

    determine the basic dimensions of the construction required and the nature

    of the materials employed therein. It follows that maximum utilization must

    be made of locally available materials, the nature and location of which were

    determined by the reconnaissance. It also follows that the location of the

    field must have been predicated upon the availability of suitable building

    materials within a reasonable hauling distance of the final location desired.

    One general aspect of the design, however, should be emphasized, and that is

    that the subgrade materials to be employed in any kind of a fill must consist

    of freely draining or highly pervious material, and that these materials must

    extend all the way out to the edge of any such fill. There must be a means of

    readily disposing of surface and subsurface drainage which may accumulate at

    the edge of the fill. It is mandatory that the subgrade be designed to contain

    well-graded gravel in its top and bottom courses in order to prevent mud,

    either above or below, from working into the central portion of the sub g rade

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    EA-I. Lang: Construction & Maintenance of Airfields

    and thus lessen its free-draining characteristics.

            The discussion on planning and design has been devoted primarily to the

    construction of heavy airfields since this type of field naturally presents

    the greatest problem. However, the basic principles of planning and design

    are also applicable to the construction of a snow and ice field, or of a

    light airfield, or a road or highway.

           

    CONSTRUCTION

            The initiation of actual construction operations is best approached by

    moving to the site, either over land or by air, an advance construction party

    consisting of personnel to complete more detailed investigation of the site

    than was possible during the period of reconnaissance, and sufficient per–

    sonnel to complete construction of base-camp facilities to be occupied by

    the main body when it arrives.

            During the reconnaissance phase a number of drill holes and test pits

    were dug to determine the general nature of the terrain and drainage pattern.

    The number of such holes and test pits must now be multiplied many times.

    For example, test holes must be drilled along the center line of each projected

    runway, taxiway, apron, and road at intervals not exceeding 500 ft. and

    preferably as close as 250 ft. Additional test holes and test pits must be

    dug throughout the area intended for building construction. This general

    area will have been selected during the planning phase, but it is a different

    matter to locate each specific building on an exact site. The variation in

    the permafrost structure may be so erratic that the shifting of a building 20

    ft. one way or the other may avoid permafrost in the foundation excavation.

    013      |      Vol_IIA-0384                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

    When major structures such as hangars are to be located, it may be necessary

    to drill on 50-ft. centers over an area of many acres to determine precisely

    the most advantageous location. Additional drill holes must be driven at

    each break in the terrain, on slopes having a variation of solar exposure,

    along streams, edges of ponds, and particularly throughout areas expected

    to be sources of borrow mat e é riel. The depth of test holes will vary. In

    general, the rule to follow is that in areas where the permafrost is not to

    be dist ru ur bed, the holes will be driven only to the surface of permafrost. In

    other areas where removal of a certain amount of permafrost cannot be avoided,

    holes should be driven at least 4 to 5 ft. below the lowest elevation of

    the proposed foundation. For large structures these holes should be driven

    to a depth equal to the distance from the hole to the nearest edge of the

    foundation. Test holes along the center line of runways, taxiways, etc.,

    must periodically be d e riven, say every 1,000 ft., to a depth of 50 ft. or

    more to ascertain the thickness and continuity of the permafrost zone which may

    lie beneath the runway. Where uncommonly large quantities of free-flowing water

    are encountered, extra holes should be driven to determine the direction of

    flow and to attempt to gain a more adequate understanding of the rate of

    flow.

            Let us turn now to the other group of the advance construction party

    assigned the mission of preparing base-camp facilities for the main body.

    The economics of such a move may not be at first apparent, but experience has

    proved that time can be gained in the long run by holding to a minimum the

    personnel so employed since they must exist initially without any base living

    facilities. At the same time, the manpower thus saved and retained with the

    014      |      Vol_IIA-0385                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

    main body back at the base of operations can well spend its time in further

    organization, planning, and making ready for the intensive effort which is

    to follow. Holding the size of the advance party to a minimum also has

    another advantage and this is to permit the establishment of well-defined

    traffic lanes through which all traffic must thereafter be required to pass.

    These traffic patterns must be rigidly [ ?] enforced. This is particularly

    true on a site covered by muskeg or tundra since any disturbance to the surface

    may induce a melting of the permafrost and the creation of a quagmire which

    may have a disastrous effect on later operations. Where construction opera–

    tions are confined to naturally exposed gravel areas, this matter of traffic

    control is not important. A second carefully controlled situation must be

    adopted at this time and rigidly enforced throughout the entire duration of

    the construction operation. This control has to do with fire-prevention

    measures. In the early phase of any construction operation in the Arctic, men

    are not acclimated to the cold and will require additional heat which will

    later not be necessary. Initial construction will be of a hasty nature and,

    therefore, more hazardous from the standpoint of fire. Adequate fire-fighting

    equipment will be lacking and conditions, in general, will be ripe for a major

    conflagration which can be disastrous to subsequent construction operations.

    The writer has learned through bitter experience that complete stocks of spare

    parts, food, clothing, and construction data can be destroyed in a matter of

    minutes. Full awareness of the disastrous effect of fires and the institution

    of immediate measures to eliminate them can be a major factor in insuring

    the successful accomplishment of the construction operations to follow.



    015      |      Vol_IIA-0386                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

            Normally, it is most advantageous to move the advance construction party

    to the site of operations during the time when the ground is still frozen.

    Some equipment and heavy items of materials and supplies can be successfully

    transported across the country without the necessity of providing special

    measures for stream, lake, and swamp crossings. Clearing and surveying

    operations can be accomplished more readily on ground in a frozen condition.

    Construction of shelter and communal facilities for the main force, and

    construction of access roads to the principal sites for borrow mat e é ri a e l are

    items of useful work that can be performed in the relatively mild weather

    before the annual spring [ ?] break-up. Completion of these items before

    the arrival of the main body means that a minimum of time will be wasted

    upon arrival of that body and that full advantage may be taken of the best

    construction season.

            The principal item of work and the greatest time consumer on an airfield

    project is the runway itself. It follows, therefore, that this feature s should

    be the first item of major work undertaken by the main construction force.

    During the planning phase an estimate of capabilities will have been made and

    a decision will have been rendered relative to the advisability of completing

    the subgrade and the pavement in one season or whether the paving can be

    deferred one year to permit consolidation of the runway fill. The latter is

    the better solution, but regardless of which solution is chosen, everything

    must be subordinated to the one all-important element of completing the

    scheduled amount of runway construction during the first season. Some curtail–

    ment of elements of the project may be occasioned by encountering unexpected

    016      |      Vol_IIA-0387                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

    difficulties. The runway must be the last item to suffer a reduction in

    effort.

            Taxiways and parking aprons, being closely allied to the runway, and being

    also major items of work, should be given second priority and attention. The

    grades established and the drainage pattern developed for the runway will

    govern grades and drainage characteristics of the taxiways and aprons. These

    problems may be mutually aggravated but should be resolved as items of impor–

    tance second only to the runway.

            The provision of basic utilities, such as adequate water supply, sewage

    disposal, power generation, roads, and fuel storage, have third priority.

            Living accommodations, including barracks, messes, latrines, washrooms,

    and dispensaries, have fourth priority.

            Airfield operational facilities, including control tower, operations

    building, crash rescue station, minor repair and shop facilities, are fifth

    in importance.

            Administrative facilities, including warehouses, cold storage, maintenance

    shops, major repair facilities, communications, and headquarters, have sixth

    priority.

            Last priority should be given to schools, training facilities, chapels,

    theaters, recreation, and other items of building construction which, while

    necessary, are not of a vital nature such as to jeopardize failure of the

    airfield mission.



    017      |      Vol_IIA-0388                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

           

    GRADING

            As previously discussed, it is preferable to avoid making cuts into

    undisturbed areas susceptible to permafrost. However, upon occasion, certain

    areas will contain humps or pinnacles which will have to be removed in order

    to preserve reasonable longitudinal and latitudinal gradients without such

    heavy fills as to make the task impossible to accomplish within the time

    allotted. One of the best times to accomplish this grading is when the air

    temperature is slightly less than 32 degrees Fahrenheit. Heavy rooters may

    be used to loosen the surface material or blasting may be employed, and the

    resultant material is removed by conventional hauling equipment. Later in the

    season after daytime air temperatures have risen above freezing, it may be

    advisable to accomplish grading in alternate areas on approximately three–

    day cycles. The material can be loosened by ripping or blasting on the

    first day. It can be left to melt and drain the second day, while the ripping

    operation is conducted in a second area. Then, on the third day, the melted

    material may be removed from the first area, and the cycle is repeated.

    Building areas may be thaw e d to greater depths if time permits by using a

    method commonly employed in gold dredging operations in the Arctic. This

    method consists of driving a large number of one-inch pipes into the ground

    on a grid pattern on 15- or 20-foot centers and pumping cold water through

    these pipes until the ground has become sufficiently thawed to permit pipes

    to be driven still farther into the ground. After the thawing has been accomplished

    to the depth required, the loose material may be excavated by conventional

    methods. Steam points may also be employed in lieu of cold water to hasten

    the rate of thawing if the time schedule must be shortened. It is important to

    018      |      Vol_IIA-0389                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

    remember that after excavation in thawed ground has been completed, it is

    necessary to restore immediately a layer of insulation to prevent the melting

    process from continuing, for the site might become such a morass that it must

    be abandoned.

           

    PREPARATION OF THE SUBGRADE

            Assuming that a section of natural terrain is available which is a suitable

    site for a runway, or that an area has been prepared by grading in the manner

    described in the proceeding discussion, then the runway may be started by plac–

    ing subgrade materials thereon, using conventional equipment and methods of

    hauling in much the same manner as airfields or roads are prepared in more

    temperate climates. The main difference to remember is that the undisturbed

    frozen soil lying immediately beneath the subgrade has great bearing value only

    so long as it remains frozen, and that a means must be provided of retaining

    this high bearing value by sealing the frozen material from heat and flowing

    water. Sealing against heat may be accomplished by preserving the natural

    tundra or moss in its undisturbed condition or by covering the frozen base

    with a much thicker layer of highly impervious gravel, crushed rock, volcanic

    ash, or other similar material. It is worth while to note that a 3-inch

    layer of moss or tundra is equivalent to approximately 36 inches of inorganic

    material. This emphasizes the importance of retaining the former if at all

    possible. Sealing against flowing water may be accomplished by providing

    diversion channels for subsurface flows and by guarding against retaining

    moisture within the subgrade by virtue of constructing in it a course of gravel

    or crushed rock of granular size such that no moisture will be absorbed

    019      |      Vol_IIA-0390                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

    through capillarity. As previously discussed, the upper and lower layers of

    the subgrade should consist of finer gravel to prevent mud from working

    into the center section of the subgrade either from above or below. It is

    important that no frozen material be placed in the subgrade. For this reason,

    it is normal that subgrade preparation be accomplished during the warmer

    months of the construction season.

            To enable the reader to have a better understanding of the thickness of

    subgrade required, and hence of the work to be accomplished, a wheel design

    load of 15,000 pounds or less will require approximately 30 inches of gravel

    in the subgrade. A wheel design load of 60,000 pounds will require approxi–

    mately 48 inches, and a wheel load of 150,000 pounds will require approxi–

    mately 72 inches. Modern aircraft requirements tend to approach the largest

    of these figures. This factor, taken in combination with the necessity for

    employing fills rather than cuts, means that, throughout the length of the

    entire runway, considerable settlement may be expected by compaction of the

    subgrade during the first year or two of its existence. The subgrade will

    be of varying depth, which means that there will be a differential settlement

    unless extreme care is taken in placing the fill material in lifts of not to

    exceed 6 to 8 inches during construction, and unless the material is

    rolled with heavy sheep’s-foot and pneumatic-tired rollers. If proper com–

    paction has been obtained during construction, and if time will permit, there

    is no reason why paving should not be accomplished the first year. However,

    limitations of time or equipment usually do not make this possible, so it is

    best to treat the surface with a temporary asphaltic seal at the end of the

    first construction season, and then the following year to regrade the surface

    and proceed with the final paving.



    020      |      Vol_IIA-0391                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

           

    PAVING

            As a general rule, runways, taxiways, and aprons built to accommodate

    present-day aircraft should be paved. Rocks and gravel picked up by pro–

    pellers and jet engines are damaging to the engines and the airplanes them–

    selves, as well as being dangerous to personnel in the area. Paving of arctic

    airfields is best accomplished by using either portland cement or asphaltic

    concrete. Limitations of time, equipment, and transportation, to say nothing

    of plain economics, almost invariably rules out portland-cement concrete.

    Also, since differential settlement may be anticipated, it is best to select

    a pavement of the flexible type, of which asphaltic concrete is the most

    suitable. Emulsions, cutbacks, and road oils are not recommended because of

    the low temperatures which do not permit proper curing. Asphaltic concrete,

    being a hot mix, can be prepared and laid even in temperatures below freez–

    ing. It is economical, quick, and simple to place, with standard equipment

    and with crews of moderate skill.

           

    SNOW REMOVAL AND MAINTENANCE

            The problem of snow removal in the Arctic is obviously one which cannot

    be neglected. However, it is not nearly as difficult as the uninitiated be–

    lieve. Equipment for snow removal, such as is employed by highway departments

    in our northern states, is entirely satisfactory. Snow crews must be organized,

    trained, and kept in readiness, day or night, during the season when snowfall

    may be expected. Snow removal operations are conducted [ ?] promptly so as to

    avoid an accumulation of packed snow greater than three inches at any one time.

    021      |      Vol_IIA-0392                                                                                                                  
    EA-I. Lang: Construction & Maintenance of Airfields

    Aircraft move with difficulty on loose snow, but without any appreciable

    trouble on compacted snow. The limit of three inches of compacted snow is

    established in order to avoid excessive slush and drainage problems during the

    spring. Deep slush might necessitate the closing down of the runway for an

    extended period. The melting of three inches of compacted snow, on the other

    hand, presents a simple problem which can be handled without difficulty.

            Runways must be regularly inspected and maintained at all times. Major

    repairs should be held over until the summer season when patching can be ac–

    complished as is normally done in the United States. There will be occasions,

    however, when emergency repairs must be made during the winter months. In

    these instances, only temporary expedients should be employed, utilizing logs,

    brush, landing mat, or built-up layers of snow and ice when no other means

    are available.

           

    James D. Lang



    Unpaginated      |      Vol_IIA-0393                                                                                                                  

    Excavations and Foundations

    EA-I. (Al T. Donnels)

    EXCAVATIONS AND FOUNDATIONS

           

    CONTENTS

    Page
    Gravel and Rock 3
    Drainage 4
    Disposal of Spoil 6
    Airfield Foundation 6



    001      |      Vol_IIA-0394                                                                                                                  
    EA-I. (Al T. Donnels)

           

    EXCAVATIONS AND FOUNDATIONS

            Excavation and foundation problems in Alaska vary greatly; however,

    there are certain basic criteria peculiar to the country with which the planning

    or construction engineer should be thoroughly familiar for the successful

    and economical accomplishment of a contemplated project. The subject

    matter of this article is proposed to encompass large-scale excavation and

    foundation factors encountered in the construction of airdromes and heavy

    structures. These factors, however, are applicable to all construction

    problems and should receive thorough consideration in the scope of planning.

            The specific location of a project immediately introduces or eliminates

    certain problems for investigation. For example, south of the Alaska Range

    no peculiar problems may be expected other than those usually encountered

    in the northern United States. Permafrost conditions do not exist south

    of the range. Depth of seasonal frost varies considerably depending on

    ground conditions, vegetation, and snow coverage. Temperature conditions

    are not severe and construction operations can be successfully carried on

    from the first of March until December, frequently throughout the year. The

    coastal regions (Prince William Sound area) have heavy snow and rough weather

    from December through March and April. Average annual precipitation in this

    area approximates 160 meters inches ; snow depths of 30 feet occurred in the winter

    of 1947-48.



    002      |      Vol_IIA-0395                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

            North of the Alaska Range, particular attention is required for the

    investigation of permafrost conditions and subsurface ice lenses. Contrary

    to popular belief among persons not accustomed to the country, snow precipi–

    tation north of the Alaska Range is comparatively light. Snow is dry and

    powdery and little or no wind occurs in the interior. Blizzards, such as

    are experienced in Montana, the Dakotas, and many other states, are not known

    in central interior Alaska. Severe temperatures may be encountered from

    December through February and March, with seasonal thaws occurring through

    April and May. Construction weather is ideal from May to November, with

    24 hours of daylight during the summer months.

            Excavation operations for air-strip construction may be started with the

    spring thaws, usually in May, although frost is still retained in the ground.

    This may be done by surface stripping with tractors and carryalls in systematic

    passes over a large area, cutting down to the frozen ground, thus permitting

    penetration of continued thaw. The operation is repeated upon return passes

    of the equipment at such time intervals as thawing will permit. In this manner

    the frost is followed downward to the desired grade in the gravel. Apparent

    hopeless mud conditions will follow until free-draining gravel is reached.

    Use of “pusher cats” should be anticipated for these mud conditions and difficult

    traction on the frozen ground.

            Permafrost may be encountered anywhere, under the seasonal frost line and

    near the surface, particularly where the ground is covered by tundra vegetation.

    It is essential that all tundra, silt, and frost-bearing material (fine mate–

    rial subject to frost action) be removed down to sound gravel base. It must be

    remembered, however, that the original thermal regime should be restored

    whenever possible. (See also “Engineering Problems and Construction in

    Permafrost Regions.”)



    003      |      Vol_IIA-0396                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

            Upon reaching the final grade for stripping operations, it is advisable

    to excavate test pits strategically located to search out sand pockets and

    frost-bearing material. These pits should be located on a grid pattern not

    exceeding 200-foot intervals and depths of 3 to 5 feet. Unfavorable condi–

    tions may require their location at more frequent intervals and slightly

    greater depths to locate the existence of ancient slough courses which are

    prevalent in the Territory and which have deposited fine sand and frost–

    bearing silts. The slough courses may or may not be discernible from the sur–

    face after stripping operations, but are readily traced by indication of

    excessive mixture of fin d — e material in the gravel. All such material should

    be carefully removed and replaced with sound gravel. Removal of this

    unsuitable material is accomplished by tracing out the slough courses with

    tractors and scrapers.

           

    Gravel and Rock

            Good gravel deposits are prevalent in practically all of interior Alaska

    and are usually found at shallow depths under the surface. Natural gravels

    are not too well-graded but are conducive to excellent subcase material.

    Gravel found in the upper Tanana Valley is relatively small — too small for

    satisfactory crushing operations. However, the gravel found closer to the

    north slope of the Alaska Range contains a fairly high percentage of coarse

    gravel (4 inches or more) that is suitable for obtaining high-quality crushed

    rock. It has been determined that the size of the gravels found is dependent

    upon the distance carried by glacial action from the bedrock of the Alaska

    Range, the gravel becoming smaller with continued grinding action beyond the

    rim of the ice.



    004      |      Vol_IIA-0397                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

            Other rock deposits in the Tanana Valley area are basalt, granite, and

    Birch Creek schist, of which the last mentioned is the most prevalent and

    usually the most accessible. The Birch Creek schist varies considerably in

    quality and, although it is not considered to be of the superior quality of

    the basalts and granites, is usable for crushing and subgrade material. It

    has a tendency to break up under compaction, forming a silty substance, and

    will not obtain the interlocking ordinarily desired for good subgrade or

    foundation construction. Economical availability may dictate its usage,

    however, but it should receive careful consideration and analysis for its

    contemplated use. It is not recommended as an aggregate in asphaltic or

    portland-cement concrete.

           

    Drainage

            The problem of drainage is one of the most important and frequently

    one of the most troublesome aspects encountered in the North. The water

    tables throughout the Territory have widely varying characteristics and

    apparently have no known relationship to the river systems. The Tanana

    Valley has a characteristically high water table, found 2 to 5 feet below

    the gravel surface, varying slightly throughout the year, and flowing slowly

    in a southerly or southeasterly direction. The water table in the upper

    Nenana Valley (mile 373 on the Alaska Railroad) was found to be approximately

    50 feet below the gravel surface and flowing in a northeasterly direction,

    although the Nenana River is above the ground surface elevation at this

    location and within 2 miles distance. The water elevation rose considerably

    in the exploratory drill holes, indicating hydrostatic pressure, although

    only sand and gravel were encountered down to the water level.



    005      |      Vol_IIA-0398                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

            The river systems have built up their silt beds in such a manner that

    natural surface drainage is away from, rather than toward, the rivers and

    their tributary sloughs. It has been observed that the gradient away from

    the rivers frequently occurs in the ratio of about 1 foot per 1,000 feet.

    Extreme meandering of rivers and sloughs is a typical characteristic.

            Further drainage and flood difficulties may be experienced in the

    spring of the year when rising rivers may wash above the surface of the ice,

    thus progressively building up thicker surface ice and higher water until

    the final ice break-up occurs. Surface drainage normally disposes itself

    rapidly through the free-draining gravel which has been stripped of the

    surface tundra. During the spring thaw, however, free drainage is prevented

    due to the ground frost and, unless other provisions for surface drainage

    are made, an accumulation of surface water may be troublesome until the ground

    frost disappears.

            Excavation for structural foundation may necessarily be carried to

    elevations below the normal water table, which adds materially to the con–

    struction problems and costs involved, for which field conditions should be

    studied in the development of plans and establishment of cost estimates. The

    proposed procedure is to confine the operation to as small an area as possible

    commensurate with available equipment, reducing the water table in this area

    by the use of well points and pumps, and repeating the operation in the next

    foundation section. The planning of subsurface installations such as base–

    ments or other adjuncts should be based on full knowledge of the specific

    subsurface and water-table conditions.

            No specific criteria exist for the solution of drainage problems. Each

    development must be worked out individually. Sloughs and marshes afford

    006      |      Vol_IIA-0399                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

    disposal of drainage water, but the problem of flood and backup water is

    present due to the usual flatness of the terrain. Freezing of drainage

    culverts and outfalls may present difficulties in blocking the runoff during

    the spring when alternate freezing and thawing occur. These should be

    located to the best advantage of exposure to permit thawing during the day.

            Sewerage and effluent trunks require installation in heated utilidors

    as being the only effective means of protection against freezing during the

    winter.

           

    Disposal of Spoil

            The matter of disposal of spoil is ordinarily not considered of major

    consequence as it falls into the routine of ordinary earth-moving operations.

    However, in the North conventional procedures frequently result in costly

    effort. Planning of operations should, therefore, carefully include the

    disposal of spoil to avoid its being handled more than necessary, or to

    prevent spoil piles from freezing, thereby forming obstructions or detriments

    to drainage or interference with other proposed operations. Removal of

    frozen spoil may be difficult and expensive and unnecessarily adds to the

    effort and cost of a construction project over the short construction season.

    Spoil piles that require subsequent removal should be removed prior to the

    onset of freezing weather.

           

    Airfield Foundation

            Pavement evaluation was made on a concrete military runway constructed

    during World War II, including the removal of slab sections for subgrade

    bearing analysis. Large voids were disclosed between the subgrade and concrete

    pavement due to settlement of the foundation. At certain locations the

    007      |      Vol_IIA-0400                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

    unreinforced pavement was unsupported for several feet and amazingly

    withstood the impact of heavy planes without failure. Whether the settle–

    ment of the foundation was due to faulty backfill containing frozen material,

    or was caused by shrinkage of permafrost under the subgrade, or a combination

    of both, is a matter of conjecture. The results, however, clearly point to

    the importance of thorough investigation in dealing with permafrost and

    placement of sound foundation material.

            In connection with the stripping operations previously described, a

    major factor in determining the final grade of the stripping operations is

    the determination of insulating coverage of nonfrost-bearing material to be

    placed over permafrost areas with due consideration given to the possible

    rising of the permafrost table under the fill. That is, it may be necessary

    to strip into the permafrost and backfill with sound material to a depth

    sufficient to obtain adequate insulation to prevent thawing of the permafrost

    from heat absorption of the runway. It may be pointed out that recession of

    the permafrost in the Tanana and Yukon valleys areas is a natural process,

    and once thawed will not return. It is understood, however, that this

    condition does not necessarily apply in some areas north of the Arctic Circle,

    in which return of permafrost may occur after thawing.

            Extensive information is available from experiments and studies conducted

    by the Permafrost Division of the Corps of Engineers for various types of

    runways and other construction in connection with heat penetration into the

    ground, depth of insulating coverage, etc. Excavation and foundation problems

    encountered in the North are closely associated with permafrost problems and

    engineers contemplating such operations are urged to avail themselves of this

    complete source of information and visit the Permafrost Experimental Project

    near the city of Fairbanks.



    008      |      Vol_IIA-0401                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

            It is entirely practicable and frequently necessary to construct

    airfields over permafrost owing to the existing pattern of the permafrost

    areas and the usual limiting circumstances in the location of airfields.

    However, in a certain selected location for an airfield in the Nenana Valley,

    the runway and development site were found to be entirely free from permafrost.

    When such conditions are encountered, it is indeed fortunate. Persons ex–

    perienced in the characteristics of the North are able to ascertain with

    reasonable accuracy the likely existence or nonexistence of permafrost by

    observation of the forests and vegetation, sloughs, marshes, water table,

    and general drainage.

            “Drunken forests” are the result of frost heaving, which causes the

    trees to assume wild angles from vertical growth, appearing to have the tendency

    of falling. Profuse growth of the native spruce stands occurs over permafrost

    areas, especially where high water tables exist. The native spruce has no

    tap root, which permits the tree to live within permafrost areas. A know–

    ledge of forestry and plant life in the North may be of much assistance to

    the engineer who is engaged in making preliminary examinations of possible

    site locations.

            Sloughs and marshes usually indicate the presence of permafrost near

    the surface. Areas subjected to good subsurface drainage are obvioualy

    desirable in all respects and are less likely to contain permafrost. However,

    such observations alone are not sufficient for determining the desirable

    location of a “site.” A likely appearing location should be further explored

    by test holes and other means applicable to the particular type of construction

    contemplated.



    009      |      Vol_IIA-0402                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

            Where extreme conditions of frost or ice action are observed, such as

    ice or frost mounds, “drunk en forest,” and areas known to contain ice lenses,

    these areas should be carefully avoided for any construction operations. An

    upset of the natural thermal balance of the permafrost table by construction

    operations may introduce insurmountable problems. The engineer confronted

    with such a task should reassure himself with the necessary field research

    and be familiar with the techniques of compensating for any upsets that would

    appear probable in dealing with permafrost conditions.

            The importance of site selection and foundation construction must be

    emphasized where permafrost exists, for there is always the possibility of a

    building filling with ice and breaking apart due to peculiarities of permafrost

    and ground water; upheaval and collapse of a building due to shifting of the

    permafrost table caused by the building itself; or foundation and structural

    failure, as occurred to the Federal Building at Nome and a major building at

    Northway and similar occurrences to dwellings and other buildings throughout

    the North.

            Subsurface ice lenses may be treacherous, for obvious reasons, if subjected

    to thawing under the foundation of an air strip of building. For an engineer

    who is involved with foundation problems a visit to the hydraulic mining

    operations along the Steese Highway, north of Fairbanks, affords an excellent

    cross-sectional view of subsurface ice lenses; here he can readily visualize

    the potential hazards involved should he risk foundation construction without

    full knowledge as to the presence of ice lenses.

            The total importance of determining the permafrost and subsurface ice

    conditions in connection with foundations lies in the simple fact that heat

    penetration into the ground may eventually reach the permafrost, causing

    010      |      Vol_IIA-0403                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

    thawing and subsequent settlement. In the case of airfields, sufficient

    insulating earth coverage may readily be constructed to compensate for the

    heat absorption at the surface. As previously described, the techniques of

    such construction and required depths of insulation are obtainable from

    precise experimental data available from the Permafrost Division, Corps of

    Engineers.

            In the case of building foundations, the heat penetration into the

    ground is normally continuous and depths of heat penetration are dependent

    upon the size of the building and other factors. For example, a small building

    or narrow building permits the influence of exterior temperatures under the

    foundation to a greater extent than would occur in the case of a building

    covering a large area. Also, the problem may be complicated by a shifting

    of the permafrost table, which may be expected to drop on the south side of

    the building due to the sun’s rays on the wall surface, and rise on the north

    side which does not receive the sun’s rays.

            The extent to which subsurface explorations may be necessary greatly

    depends upon the type and permanence of the buildings contemplated. Thawing

    temperatures may be expected to penetrate the ground beneath a building at

    the rate of from 3 to 5 feet per year under average conditions for depths

    within the limits of average building construction. Thermal penetration

    becomes slower with increased depths. Where permafrost is know to exist at

    20- to 3 0 -foot depths, no serious foundation settlement would be expected

    within the usable life of temporary or semipermanent installation. Numerous

    military installations constructed over known permafrost areas during the war

    have shown no indication of settlement up to the present time. It is probable

    that sufficient time has not elapsed to permit thawing temperatures to reach

    011      |      Vol_IIA-0404                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

    the permafrost and cause settlement to a perceptible degre — e .

            The element of time is usually a major factor in the construction of

    temporary or semipermanent military installations. For a construction

    program of this nature, extensive foundation examinations would be imprac–

    ticable and unwarranted.

            Heavy structures or buildings of a permanent character, such as hangars,

    power plants, or comparable major buildings, to which settlement would

    seriously endanger structural or mechanical alignments, should not be con–

    structed over permafrost. The foundation conditions for such structures

    should be thoroughly investigated and the structure located in an area

    devoid of permafrost.

            The following test was made to ascertain whether or not appreciable

    settlement would occur upon thawing of permafrost-bearing gravel and to

    determine to what extent such permafrost-bearing gravel could be used for

    foundation.

            The ground was stripped of all surface material to sound gravel within

    the permafrost table over an area sufficiently large to conduct the test

    properly, and depressed sufficiently to contain water. Two 1-inch diameter

    pipes about 5 feet long were welded to the inside bottom of a 55-gallon steel

    drum in such a manner that the pipes were parallel, about 2 feet apart and

    extending out of the open top of the drum. The drum was then filled with

    concrete to obtain substantial weight. Welding the pipes to the bottom of

    the drum prevented transmission of movement to the pipes from shrinkage of

    the concrete. A heavy steel leveling plate was placed on the frozen gravel

    surface and the concrete-filled drum placed thereon. Two pipes were securely

    embedded into the permafrost on each side of the drum in vertical position.

    012      |      Vol_IIA-0405                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

    A rigid steel angle was secured between these pipes. The steel drum was

    adjusted to position so that the pipes extending therefrom were aligned with

    the angle beam. Two micrometer dials (Ames) were secured between the angle

    beam and the pipes extending from the drum in such manner as to register

    movement of the drum. Water was placed in the depression, partially submerging

    the drum, and heated by steam from a portable boiler. Care was exercised to

    apply heat evenly around the drum to obtain uniform settlement. The results

    of the test indicated a settlement of approximately 1 inch in 5 feet of thawed

    ground.

            Upon examination, the frozen gravel might give the impression that thawing

    of the frost crystals in the voids would have little or no effect on the

    shrinkage of natural compacted gravel, thus leading to the false assumption

    that such material would be conducive to good foundation.

            The results of the above test, however, indicated that a settlement of

    6 inches or more may be anticipated in event of thawing of a permafrost lenso

    of average thickness encountered in this particular area. This a mount of

    settlement could obviously be disastrous to a large rigid structure.

            Such ground would afford suitable foundation for light frame structures

    of the temporary or semipermanent type to which no serious damage would result

    that could not readily be repaired in event of slight settlement. This effect

    should be considered in the installation of plumbing and utility connections.

            The selection of a site location for a major structure entails the primary

    consideration of locating an area void of permafrost. If such an area cannot

    be located, the permafrost under the foundation area must be thawed which

    involves a difficult and time-consuming operation. The exterior foundation line

    013      |      Vol_IIA-0406                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

    line should not be less than 20 feet horizontal distance from a permafrost

    body. The permafrost occurs in the form of islands or “kidneys” interspersed

    with void areas. The determination of these void areas involves a considerable

    amount of subsurface exploration. In the course of master planning, the plan–

    ning engineer should allow adequate flexibility to permit the shifting of site

    locations, if possible, to such a void area.

            Exploration for the existence or nonexistence of permafrost by drilling

    alone is exceedingly time-consuming. In order to speed up this operation,

    the following method was satisfactorily utilized for establishing the location

    for a hangar having 90,000 square feet of floor area.

            The proposed building site was surveyed and s taked out (exterior foundation

    line plus 20 feet). At each corner and at quarter points on each side and at

    the center, railroad rails were drive d n with a drop-hammer pile driver. Explora–

    tion was carried to a depth of 60 feet, as it was considered that no permafrost

    would exist beyond this depth, or if it did, it would not be reached by heat

    penetration. Upon striking permafrost, no further penetration of the rail

    could be obtained. Permafrost was struck along one entire side of the building

    site and partially along the two adjacent sides. No permafrost was found else–

    where on the building site. This indicated that the permafrost lens out somewhat

    diagonally across approximately one-quarter of the building site area. It then

    became necessary to locate and plot the edge of the permafrost lens. The dis–

    tance between the rail points which straddled the edge of the lens was bisected,

    and a rail driven at that point. This procedure was repeated on a grid pattern

    until the edge of the lens was located to an accuracy of approximately 5 feet.

    Concurrently with the driving operation, well drills were used at strategic

    locations to penetrate through the permafrost, measuring depth and thickness

    014      |      Vol_IIA-0407                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

    of the lens, and also to verify the conditions where indeterminate rail

    driving was encountered due to striking dense material or rocks. The tops

    of the lenses were found at 15- to 30-foot depths and were from 20 to 30 feet

    in thickness and usually tapered off toward the edge of the lens.

            Establishment of the exact location of the permafrost lens afforded

    knowledge of the required distance and direction to shift the building site.

    Shifting the building site off the permafrost area also introduced the possi–

    bility of moving the opposite side of the building onto another permafrost

    island, which condition required investigation. Further possibilities as to

    existence of permafrost islands within the building area also required investi–

    gation. This method required comparatively few drill holes and the entire

    work was accomplished in about two weeks.

            The rail-driving method had not been previously attempted and some experi–

    menting was required to effect efficient operation. Rails were cut from 10-

    to 15-foot lengths, which was the maximum length that could be placed in the

    driving leads. Upon driving to ground surface, a new length of rail was placed

    in the leads and spliced to the driven rail by welding. Some difficulty was

    experienced in the welds breaking or the rail bending under impact of the hammer.

    The development of a more efficient splice and the improvision of a lead guide

    to prevent bending corrected this difficulty. The driving method could be

    greatly improved and the operation speeded up considerably with the planning

    of an efficient equipment setup and manner of splicing. Several pile drivers

    with swinging leads and well drills are required to cover efficiently the extent

    of the work.

            The use of geophysical equipment was considered for determining the location

    of permafrost. However, the time involved for procurement of special equipment

    015      |      Vol_IIA-0408                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

    and experienced operating personnel, together with the fact that such an

    operation would be experimental with questionable reliability of results,

    precluded its use d for the above operation. It is possible that the use

    of geophysical equipment for such purpose on extensive operations might

    prove of extreme value in saving time and labor, and introduce further

    knowledge of subsurface conditions.

            In the event that it is not possible to obtain a site location entirely

    devoid of permafrost and it becomes necessary to thaw out such an area, the

    site should be located to minimize the quantity of permafrost to be thawed.

    The method of thawing permafrost by percolation of cold water as observed in

    connection with mining operations in the Fairbanks and Nome areas would

    ordinarily not be considered practicable for construction operations owing

    to the time involved, unless a long-range, extensive construction program was

    contemplated.

            Although the experience of the writer did not entail the necessity of

    performing thawing operations, as it was easier to move off permafrost areas,

    a planned operation was conceived by driving steam points on a grid pattern of

    10 to 15 feet over an area of not more than 100 feet square and connected to a

    header system to which steams would be supplied from portable steam boilers.

    It was calculated that this interval of steam points would adequately raise

    the ground temperature to permit rapid thawing and permit continued penetration

    of the steam [ ?]

    points by hand-driving similar to the method used on cold-water points, which

    consists of a weighted mandrel slipped over the projecting pipe similar to

    that used in driving steel fence posts.



    016      |      Vol_IIA-0409                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

            The primary subject of excavation and foundation requires a complete

    correlation with all other factors in planning and construction. Such

    planning may be required in considerable detail for the effective operation

    of the work. An extensive amount of preliminary field investigation may be

    necessary for the development of master and detail planning. The procurement

    and transportation of equipment, materials, and personnel involve the thorough

    planning of logistics, particularly in connection with the heavy equipment

    necessary for excavation and foundation construction like power shovels, tractors,

    carryalls, dozers, rock crushers, and trucks. Shipping and unloading facilities

    for quantities of such equipment at Alaska ports are limited. The ports of

    Seward, Whittier, and Anchorage are the only territorial ports with railroad

    connections. These ports at present (1949) have limited dock facilities. The

    port of Anchorage is usually icebound during the winter months. Inland trans–

    portation is subject to limited highway facilities to off-rail points.

            In addition to the solution of transporting such equipment, it becomes

    necessary to set up adequate shops and self-sufficient facilities for equipment

    repair and maintenance. Excessive equipment deadlines have been evidenced on

    past operations for lack of adequate planning for this phase of work.

            Concurrent with the above requirements are those necessary for the housing

    and care of personnel. These further tax the facilities for mat e é riel procurement.

            Air transportation in the North is vital. In remote sections of the

    territory, the primary operation of grading off a temporary airfield for use by

    medium-sized planes will be found to enhance greatly communications and security

    in providing the means of obtaining much needed supplies when starting and con–

    ducting operations on a project.



    017      |      Vol_IIA-0410                                                                                                                  
    EA-I. Donnels: Excavations and Foundations

            All of these considerations require precise planning and coordination

    to effect full advantage of operations during the relatively short construction

    season. The failure of any one major factor may easily result in the partial

    or total loss of a year’s operation, which delay may be the determining

    element of success or failure of the project.

           

    Al T. Donnels



    Unpaginated      |      Vol_IIA-0411                                                                                                                  

    Emergency, Temporary, and Semi-permanent Housing for Polar Areas

    EA-I. Palmer V. Roberts

    EMERGENCY, TEMPORARY, AND SEMIPERMANENT HOUSING FOR POLAR AREAS

           

    TABLE OF CONTENTS

    Page
    Emergency Housing 2
    Principles of Design of Temporary and Semipermanent Buildings 11
    General 11
    Insulation 14
    Condensation 20
    Methods of Condensation Control 23
    Ventilation 28
    Temporary Housing 30
    Semipermanent Housing 35
    Prefabricated Housing 35
    Modern Prefabricated Buildings 40
    Bibliography 47



    Unpaginated      |      Vol_IIA-0412                                                                                                                  
    EA-I. Roberts: Housing

           

    LIST OF FIGURES

    Page
    Fig. 1. Steps in building a snow cave 3-a
    Fig. 2. Steps in domeshaped snowhouse construction 6-a
    Fig. 3. Steps in domeshaped snowhouse construction-continued 6-b
    Fig. 4. Steps in earth and wood house construction 30-a
    Fig. 5. Typical section Quonset hut (Barrow) 40-a



    001      |      Vol_IIA-0413                                                                                                                  
    EA-I. Palmer W. Roberts

           

    EMERGENCY, TEMPORARY, AND SEMIPERMANENT HOUSING FOR POLAR AREAS

            It is a fundamental principle in building design that the best buildings are

    those so constructed throughout that they meet the basic requirements of the region

    while also serving the operational requirements of the users. The type of design

    selected depends greatly on local soil, drainage, and climatic conditions. The

    details of the design depend greatly on the materials locally available or trans–

    portable to the area. Therefore, standards for the construction of shelters and

    buildings in the Arctic and Subarctic, and particularly where permafrost is present,

    will vary greatly from those applicable to the temperate and tropic zones. In

    areas where permafrost does not exist, the construction of housing may be similar

    to that of any region of cold winters where seasonal frost action is severe.

            The selection of an appropriate type of housing in the Arctic is perhaps best

    approached by the consideration of three factors: the length of time the build–

    ing is to be occupied, the time required for construction, and whether or not

    local or transported materials are to be used in the construction.

            Various classes of housing may be defined on the basis of these factors as

    emergency, temporary, semipermanent, and permanent. The following definitions have

    been arbitrarily established for the purpose of providing an orderly approach to

    the subject of arctic housing:



    002      |      Vol_IIA-0414                                                                                                                  
    EA-I. Roberts:

            Emergency: to be occupied for a period ranging from overnight to possibly

    as long as one year, and capable of being completely constructed in less than

    half a day from materials available on the site, or with lightweight materials

    brought in for construction purposes.

            Temporary: to be occupied from one to five years and requiring approximately

    one day’s effort for construction, using local or imported lightweight building

    materials.

            Semipermanent: to be occupied for at least 15 years, requiring more than

    one day’s construction effort, and utilizing lightweight prefabricated materials

    brought into the area for the building.

            Permanent: to be occupied for at least 25 years, requiring considerably more

    than one day’s effort for construction, and using high-quality prefabricated or

    on-site fabricated imported building materials of a standard nature.

            Discussions here will be concerned only with the first three classes of

    buildings, which are generally of one-story construction. Permanent buildings,

    of course, follow the same principles; but as this type of construction largely

    conforms to standard construction in the northern United States, it will not

    be dealt with in this discussion of arctic housing.

           

    EMERGENCY HOUSING

            In an emergency, many [ ?] types of shelters and windbreaks can be constructed

    from materials at hand. One may first utilize the materials with which one has

    landed. If one came by plane, any of the easily removable sections, such as the

    cowling, will serve for construction. The cabin of a large plane will serve as

    an excellent temporary shelter. Similar use may also be made of stranded vehicles

    and boats. Any large piece of fabric may be used as a shelter roof, and the sides

    003      |      Vol_IIA-0415                                                                                                                  
    EA-I. Roberts: Housing

    can be built up with snow blocks, sod, etc. Snow, soil, stone, bones of large

    mammals (whales), and wood, if available, will furnish building material for

    housing once the immediate crisis is over.

            The types of shelter that may be improvised by one or more men are numerous.

    Tents may be made from shelter halves or parachutes. If deep drifts are found,

    snow caves may be built to good purpose. Walls of snow blocks will serve as wind–

    breaks. Standing or fallen trees may be most useful for individual survival.

    Within a shelter, some form of insulation must be placed under a fire if the

    floor of the shelter consists of snow; good insulation is required under a sleeping

    bag or other bedding.

            Snow Cave . One of the simplest forms of shelter is the snow cave. Such a

    cave can often be built by two men in about two hours. The only tools required

    are shovels. A square of canvas or other fabric may be useful to cover the door.

            A site is selected on a reasonably steep slope where the snow has lain

    in place long enough to have become compacted. ( See Figure 1. ) A working shelf is

    cut into the slope or drift, and then a small cave two feet by two feet is ex–

    cavated back for a foot or two; this becomes the doorway. The cave proper is then

    started, working gradually upward, as the floor of the cave should have an upward

    slope , away from the doorway. The easiest procedure may be to cut the snow into

    blocks and cast them out through the doorway and down the slope. The ceiling should

    be shaped into an arch or done. This allows condensation to run down the walls,

    provides standing room in the center, and serves to strengthen the shelter.

            The final cave size, to accommodate three or four people, should be about five

    feet high, nine feet long, and eight feet wide. A sleeping place is arranged by

    having the level of the bed platform at least one foot above the floor, which

    003a      |      Vol_IIA-0416                                                                                                                  

    FIGURE 1



    004      |      Vol_IIA-0417                                                                                                                  
    EA-I. Roberts: Housing

    should be terraced. After this, the shovels and all personal equipment are brought

    into the cave, a ventilating hole is cut upward through the roof, and, if the

    entrance is not low enough, a square piece of fabric is placed to form a door.

    If the bed platform is some two feet higher than the top of the entrance, it

    will not be necessary to close the door, unless there is a strong wind that

    forces gusts into the cave. For, cold air being heavy, it will remain at a low

    level so long as the upper parts of the cave are filled with warm air.

            A snow cave has many advantages over the tent, among them that the material

    to be transported is lessened by the omission of the tent and stove. Once the

    cave is occupied, the air within rises to a temperature above freezing and remains

    there as long as the cave is occupied, no heating being required except that fur–

    nished by the bodies of the occupants. In the daytime no lighting is needed,

    for sufficient light filters through from overhead; at night a single candle

    gives enough light, because of the high reflecting qualities of walls and ceiling.

            Snow caves have been successfully used in the Arctic as well as in high

    mountains. Instruction in their construction and use should form part of the

    normal training of polar travelers.

            The dome snowhouse is built from domino-shaped blocks of wind-pressed snow.

    These blocks are cut four to six inches thick, twenty to forty inches long, and

    from twelve to twenty inches wide. Such blocks, depending on the density of the

    snow, weigh from fifty to a hundred pounds and are strong enough to support not

    only their own weight but also that of the blocks resting on them. It is of prime

    importance that the snow be of the proper consistency. This can be determined

    by driving a blunt but slender rod into a snowbank with a steady shove. If it

    sinks in slowly with an even pressure, the snow is of the proper consistency for

    005      |      Vol_IIA-0418                                                                                                                  
    EA-I. Roberts: Housing

    use in construction. Snow that is too soft crumbles in handling; if layers are

    of uneven hardness the blocks may split; if the snow is too hard the blocks will

    be poor insulators and the house will be cold.

            In the building of a snowhouse the only tools required are a knife with a

    blade fourteen to twenty inches long for cutting blocks, a shovel for piling snow

    on the completed house, and a rod for determining the consistency of the

    snow. For cutting blocks from very hard snowdrifts, a carpenter’s saw is good.

    Three or four men make a desirable building team: one cutting the blocks, a second

    carrying the blocks and chinking cracks, and the third working inside the house,

    building. A fourth man, if available, may work outside the house, chinking cracks

    between the blocks, but not following the builder too closely, for snowhouse

    walls are fragile until the soft snow pressed into the cracks has had time for

    setting into snowcrete.

            The best location for building a snowhouse is on a level part of a well–

    compacted drift where the snow is more than three feet deep. This depth provides

    ample insulation and permite tunneling the entrance under the walls to a well in

    the floor, which, as later explained, is the preferred entrance construction. If

    this desired depth of snow is not available, then an entrance porch may be built

    from snow blocks aboveground, whereupon it will be necessary to close the house

    door at night, as a gravity differential will not be available for keeping the

    cold air out. If the house is to be built on bare ground, a floor of at least

    a five-inch layer of compacted snow must be placed to form an insulating layer;

    for bare ground radiates cold.

            The usual snowhouse is dome-shaped, with a five- to seven-foot ceiling, and

    has a diameter equal to twice its height. A house can be built to accommodate ten

    006      |      Vol_IIA-0419                                                                                                                  
    EA-I. Roberts: Housing

    people, if the snow is good and the builder skillful; but such a house will have

    to be so high that it will necessarily be cold, since the warmest air will gather

    up in the dome where it is of no comfort to the occupants and threatens to melt

    a hole in the snow roof.

            The first step in building a snowhouse is to lay out a circle. For a

    twelve-foot house this will have a six-foot radius. ( See Figure s 2 . and 3) The first row

    of blocks are stood on edge, fitted together around the line of the circle, and

    tilted slightly inward. The first course is tapered in height by cutting with

    the knife, and succeeding blocks are laid in a continuous spiral, tilting farther

    and farther inward until there is only a small opening left at the top of the

    dome. Then the builder carves what is named the king block, and, from the inside

    of the house, thrusts it out edgewise through the aperture; he then levels the

    block and lets it sink into place. The builder on the outside of the house chinks

    the openings between the blocks, gently but firmly, with loose snow, which begins

    to set into snowcrete. After all blocks are set in place, the final chore is to

    throw loose snow over the completed house with a shovel, taking care to get none

    struck on the very top of the dome. This snow slides down and forms, as it

    finds its natural angle of repose, a banking perhaps three feet thick at the

    base, thinning upward.

            The door is provided by tunneling under the wall to the well inside the house.

    A bed platform, occupying about two-thirds of the interior floor space, is built

    of snow. The level of this platform is at least eighteen inches above the top

    of the entrance, as this is required for gravity control of the temperature

    within doors. This eighteen-inch minimum difference relationship between the

    level of the bed platform and the entrance is always strictly adhered to, other-

    006a      |      Vol_IIA-0420                                                                                                                  

    FIGURE 2



    006b      |      Vol_IIA-0421                                                                                                                  

    FIGURE 3



    007      |      Vol_IIA-0422                                                                                                                  
    EA-I. Roberts: Housing

    wise a closure for the door would be required.

            For sleeping, the bed platform is covered with some good insulator, such

    as a double layer of skins, with the fur side down on the bottom skin and up on

    the top one. This arrangement prevents body heat, which would cause thawing,

    from passing to the snow underneath.

            Warmth for the snowhouse is provided by the use of an alcohol or seal oil

    lamp, or by a kerosene or gasoline stove. The colder the weather the hotter the

    house may be kept without melting the roof, for the cold from outside penetrates

    into the snow blocks to meet the heat from within and prevents melting. To glaze

    the inner wall surface, the temperature in the house is raised high, immediately

    after bedding has been placed in position; the inner surface of the walls, which

    absorbs moisture like blotting paper, now becomes spongy. Then the fire is put

    out, or a large hole is made in the roof, and the inner wall is allowed to freeze.

    This glazes the inside with a film of ice, provides a hard protective inner sur–

    face which does not crumble when the occupants touch it, and greatly increases

    the strength of the dome.

            Ventilation is controlled by the gravity method. A wooden chimney or

    vent is placed in the dome, a little off center. When the lamp or stove is not

    burning, the vent is closed by stuffing mittens or a cloth in the vent, but when

    fires are in use the vent is opened as required. The upward movement of warm

    air through the vent allows cold air to enter from below through the door passage.

    Through this method the rate of change of air and the temperatures of the room

    are controlled.

            The interior of a snowhouse is sufficiently illuminated to permit the carry–

    ing out of routine tasks during daytime hours by daylight passing through the

    008      |      Vol_IIA-0423                                                                                                                  
    EA-I. Roberts: Housing

    translucent walls. The full moon in a clear sky also gives enough light inside

    the house for dressing and even for cooking. During periods of darkness, the

    inside of the house can be illuminated by one ordinary candle, for the light is

    reflected from the many crystalline surfaces of the snow dome, diffusing uniformly.

            The principal advantages of the snowhouse are that the transportation of

    building material or tent is not required, no additional equipment is needed for

    construction, four men can build [ ?] a comfortable camp big enough for six in a

    little more than an hour, any adaptable man can be taught snowhouse-building in

    one day, a minimum of heating is required to maintain a livable temperature,

    clothes stay dry, and the dwelling is practically soundproof to such noises as

    men shouting or dogs barking, permitting more restful sleep.

            Though the dome snowhouse was probably an Eskimo invention, it was never

    universally used by them. It seems likely that, before the coming of Europeans,

    more than half the Eskimos had never heard of a dome snowhouse, or had learned of

    it only by remote hearsay. Possibly less than twenty per cent of them had lived

    in such houses, and then only during periods of intense cold. Perhaps another

    ten per cent knew how to build snowhouses, but used them only in emergency.

    Geographically, the dome d snowhouse was formerly unknown, unless by hearsay, to

    Eskimos in northeastern Siberia, in all of Alaska, and in all of Greenland except

    the extreme northwest corner, north of Melville Bay. Nowadays all Eskimos know

    of the snowhouse through reading, photographs, and movies. The best snowhouses

    are built in the area between King William Island and Coronation Gulf, in the

    Canadian archipelago , and on the mainland.

            We cannot, therefore, expect that Eskimos in every area will be able to

    009      |      Vol_IIA-0424                                                                                                                  
    EA-I. Roberts: Housing

    construct proper snowhouses. Accordingly, travelers and intending northern

    residents should learn the art of constructing this type of temporary housing

    themselves. In Sweden, since 1933, dome-shaped snowhouses have been successfully

    used by skiers who tour the mountains, and they were early introduced to the

    Swedish army; since about 1940, the construction of snowhouses has been taught

    the armed forces of most countries that engage in exercises in polar and subpolar

    regions.

            Tents have long served as dependable shelters, and both fabric and skin tents

    have been widely used in the Arctic. While the warmth of a tent, like clothing,

    depends on air spaces, it does not seem practical with fabric tents to have these

    air spaces within the fabric itself. The desired insulation quality is therefore

    secured by the use of lightweight windproofed double tents. Skin tents derive

    their warmth largely from the air spaces between the hairs, and, in the case of

    caribouskin tents, additional warmth is provided through the hairs themselves,

    these being hollow and filled with air. Under extreme cold conditions, double–

    layer skin tents are used and so erected as to allow about a one-inch layer of

    air between the skins. This is accomplished by placing the fur sides of the skin

    toward each other.

            Dome or umbrella-shaped tents are to be preferred over peak-shaped ones such

    as the tepee (tipi), ridge, or pyramidal forms. Peak-shaped tents allow the

    warmth to gather at the top of the tent where occupants do not have the benefit

    of the heat. However, peaked tents are greatly improved in warmth if a false

    ceiling of fire resistant fabric is placed not more than seven feet above the

    floor, to prevent the heat from rising to the peak. Floors for tents, if provided,

    010      |      Vol_IIA-0425                                                                                                                  
    EA-I. Roberts: Housing

    should be furnished as a separate piece, or pieces, from the rest of the tent.

    Floors attached to the walls of tents soon become covered with frozen condensa–

    tion and snow, and cannot be cleaned easily. Conventional flap-type openings,

    with ties in the front of the tent, provide a more satisfactory entrance than the

    door which ties shut like the mouth of a duffle bag. The latter works only when

    the material is either not frozen or else frozen and dry. When moisture gets into

    the entrance, at below zero temperatures, the mouth of the bag becomes increasingly

    difficult to tie and finally becomes entirely inoperative.

            All tents for per s onnel should be provided with stoves, especially where

    driftwood is abundant on a coast or along a river, or where bushes and trees grow.

    Asbestos insulation should be placed around the aperture in the overhead layers

    of canvas or skin through which the stovepipe passes. This asbestos should extend

    at least four inches beyond the stovepipe. For wood-burning stoves the top–

    most length of stovepipe should have a medium-mesh wire screen to keep sparks

    from falling on the tent and burning holes in it; or a fireproof material should

    be used.

            Guy-rope fastening tabs should be reinforced. Guy ropes should be made of

    nylon and should be provided with a toggle at the end of each rope. These toggles

    may be buried and tamped into the snow or frozen into a trench out into the ice.

    The use of deadmen is often advisable. If tent pins are used, a light weight

    metal tent pin is preferred to wood or other such material, as the metal pin

    may be driven into ice or moderately hard earth without damage.



    011      |      Vol_IIA-0426                                                                                                                  
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    PRINCIPLES OF DESIGN OF TEMPORARY AND SEMIPERMANENT BUILDINGS

           

    General

            Important factors which will influence the design of buildings are the

    materials available; the temporary or permanent nature of the construction; the

    time available in which to construct; the purpose for which the buildings are to

    be used; and the location and orientation of the structures. The operational

    requirements will, in many cases, determine the type of building that will be used,

    but the fundamental principles that influence the design will apply to all build–

    ings. All housing should provide adequate space, utility, heating, insulation,

    ventilation, and , if required, portability. All building construction in the

    Arctic and Subarctic must meet certain basic - requirements peculiar to these

    regions. These requirements are fixed by the special climatic, geological, and

    topographical conditions, such as low temperatures, high winds, drifting or

    deep snow, long periods of cold, absence of direct sunlight in midwinter and of

    darkness in midsummer; foundation conditions affected by permafrost and related

    phenomena; and poor drainage. (See “Work Feasibility.”) As a consequence, all

    polar building design and construction possess certain common factors and

    characteristics.

            Foundations for buildings to be erected in permafrost or adjoining areas

    should be carefully designed after considering all factors. (See “Engineering

    Problems and Construction in Permafrost Regions” and “Excavations and Foundations.”)

            Surface and subsurface drainage under the buildings must be avoided entirely

    or [ ?] else it must be adequate in all seasons for conveying surface and groundwater

    away from the site.



    012      |      Vol_IIA-0427                                                                                                                  
    EA-I. Roberts: Housing

            Building frames must be designed and constructed to resist stresses caused

    by high winds. Resistance to high wind velocity, where required, may be pro–

    vided by designing for a 20 lb./sq.ft. wind load, and, in areas of extremely

    high winds, roofs should be anchored by guys. Consideration should be given to:

    1. Anchoring walls or structures to foundations by bolts, reinforcing

      steel, deadmen, cables, or cleats.

    2. Tying roof trusses and rafters securely to the frame.

    3. Using knee-braces to prevent the frame from leaning sideways.

    4. Using diagonal sheathing for rigidity.


            Roofs must be able to withstand strong winds and heavy snow loads. Both

    may occur at the same time. Roof framing should be designed for a snow load of

    30 lb./sq.ft. and strengthened if partial clearing of snow is not possible.

            The outer shell of the building must be impervious to wind, rain, and snow.

    High winds have a destructive effect on roof coverings, particularly on the low–

    pressure leeward side. The best roofs are metal, laid from the leeward to wind–

    ward side and coated with hot asphalt. Another satisfactory roof is the built-up

    type, consisting of a base sheets of 30- to 90-lb. bituminous-saturated felt

    nailed with large-head roofing nails spaced not more than 6 inches apart horizon–

    tally and 12 inches apart vertically, followed by one or two layers of 15-lb.

    bituminous-saturated felt mopped on to the base sheet with hot asphalt, over

    which battens or wood strips must be nailed to hold down the covering.

            Eaves . Where there are extremely high winds, eaves should not be used.

            Insulation must be complete throughout walls, ceilings, and floors to insure

    proper heat retention, and to prevent the thawing of the permafrost under the

    building.



    013      |      Vol_IIA-0428                                                                                                                  
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            A ventilated air space must be provided between the building floor and the

    ground, or an insulated cover must be placed on the ground, before the floor

    is laid, to preserve the thermal equilibrium of the ground and prevent thawing

    below the foundation base.

            Positive ventilation and circulation of air must be maintained at all times.

    This may be accomplished by the proper use of windows, doors, and vents. Window

    and door openings should be small and as near the ground as is possible, to

    minimize the loss of heat, and aid in controlling ventilation. All ext r erior

    doors should open inward, as outward-opening doors may be blocked by snow, barring

    egress, or blown off by high winds. Double doors or a storm vestibule must be

    provided for each entrance, unless gravity control of air is used.

            Heating . All personnel, administration, and shop buildings, and many

    storage buildings, require heating. Due to the cost of construction of distribu–

    tion systems, and heat losses incident thereto, individual heating units are

    preferred, except for large installations. In the Arctic, due to the scarcity

    of wood, coal- or oil-burning stoves are used; south of the tree line, coal-,

    oil-, and as well as wood-burning stoves also may also be provided. (See Mechanical-Electrical

    section for discussion on this subject.)

            Fire-fighting measures and fire prevention should be carefully considered

    in regard to all buildings and installations.

            Clothes-drying facilities are required for all buildings housing personnel.

    These may be provided near the entrance to sleeping quarters; where possible, warm

    air used to dry the clothes should be exhausted from the building.



    014      |      Vol_IIA-0429                                                                                                                  
    EA-I. Roberts: Housing

           

    Insulation

            By “insulation” is meant material used, in addition to ordinary building

    materials, for the purpose of retarding the flow of heat through the walls,

    floors, or roofs of buildings. (Insulation is also used to reduce the transmis–

    sion of sound through walls, partitions, ceilings, or floors, but sound insula–

    tion is not considered in this article. ) The primary purpose of thermal insula–

    tion is to permit the maintenance of the desired interior temperature in an

    economical manner, to keep buildings warmer in the winter by reducing heat

    losses, and to keep them cooler in the summer by reducing the penetration of heat

    from the outside. While maintaining the desired interior temperatures, insula–

    tion is a major factor in retarding or preventing condensation and [ ?] decreasing

    or eliminating drafts.

            Obviously, good insulation results in fuel economy during cold weather.

    Heat losses occur in a building by conduction and by air passing through cracks,

    doors, and windows. Insulation retards this flow of heat.

            Ordinary building materials have some insulating value, but are not nearly

    as effective as the special insulating materials we shall discuss. For example,

    1 inch of insulation board retards the flow of heat as much as 2 to 3 inches of

    lumber, 15 inches of brick, 23 inches of cement plaster, or 37 inches of concrete

    made of sand and gravel.

            Types of Insulation. Various substances are used as insulation material.

    The substances most commonly used are vegetable or mineral products. As a general

    rule, greater insulation is obtained from the lightest weight materials. Ordinar–

    ily, lightness in weight is attained by entrapping tiny air cells in and between

    the insulation substances. Heat travels relatively slowly through these air spaces,

    015      |      Vol_IIA-0430                                                                                                                  
    EA-I. Roberts: Housing

    since air is a very poor conductor. Insulation materials are manufactured in

    various forms and shapes for case in application. They fall into the following

    general classifications.

            1. Flexible Insulation. This type of insulation is made of materials

    manufactured into flexible blanket, quilt, or bat form, usually with a nailing

    flap along each edge for fastening between ribs or studs. The materials most

    commonly used for flexible insulation are: aluminum foil (see under “Reflective

    Insulation”); animal hair, available as 100% pure hair or mi s x ed (felted) with

    other fibrous materials, such as asbestos or jute, and stitched between sheets

    of kraft paper; cotton, flameproofed and backed with water-resistant paper;

    eel grass, a marine growth, processed and stitched between kraft paper; glass

    fibers, interlaced into a wool d -like mass and backed with water-resistant paper;

    mineral wool, felted from rock wool fibers and encased in water-resistant paper;

    rock wool, blown from molten rock or molten furnace slag and encased in kraft

    paper; wool fibers, manufactured into cre e p ed individual plies which are stitched

    together, treated for fireproofing, and encased in water-resistant paper, or

    asphalt-treated and flameproofed.

            2. Loose Fill or Blow-on Insulation. This type of insulation is made in

    loose form. Installation is accomplished by filling the spaces between ribs or

    framing members or by blowing it onto the inner surface of the outer covering

    and on structural members. The most commonly used materials for loose or fill

    type insulation are: cellulose fibers, mixed with adhesives when blown on;

    cork, granulated or in powder form; redwood bark, ground into fleecy fibers;

    rock wool, granulated or in loose form for either fill or blow-on; vermiculite,

    mica ore, highly expanded by heat; wood pulp, processed to resist fire, moisture,

    and vermin.



    016      |      Vol_IIA-0431                                                                                                                  
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            This type of insulation is not recommended for use in walls where the outer

    or cold wall surface is more resistant to the passage of moisture vapor than the

    inner or warm wall surface of the building. This insulation is pri m n cipally used

    on horizontal surfaces, as above ceilings and for filling wall cavities where

    access is a problem.

            3. Rigid Insulation. Materials are manufactured into rigid shapes of

    varying thicknesses and marketed as corkboard, insulating building board, insulat–

    ing lath, insulation plank, insulation sheathing, insulation tile, insulation

    plaster or concrete, and roof insulation. The materials most commonly used are:

    cane fibers, waterproofed and felted together; cork, compressed under heat; glass

    fibers, compressed under heat and parcels coated with a waterproofing compound;

    v V ermiculite, mica ore highly expanded by heat and mixed with plaster or cement;

    wood fibers, felted together and pressed into solid form, usually treated for fire,

    moisture, and vermin resistance.

            Rigid insulation gives good results when used in temporary and prefabricated

    building, as discussed in this article. It insulate d s the inner flanges of the ribs

    or studs, and, since it is rigid, generally serves as an interior lining as well

    as insulation.

            4. Reflective Insulation. This type of insulation is distinguished from

    the other types in that its effectiveness is based on its ability to reflect

    radiant heat waves. Reflective insulation, therefore, should be installed with

    the reflective surface exposed to an air space. Reflective insulation is made

    into thin sheet or foil form and generally applied between the structural ribs or

    studs and rafters. Materials most commonly used for reflective insulation are:

    aluminum foil (thin sheets) or foil backed with a kraft paper; foil on one or

    both sides of kraft paper laminated with asphaltum; foil separated by air cells

    which are formed by crimped paper; foil laminated to [ gyp ?] gypsum wallboard,

    017      |      Vol_IIA-0432                                                                                                                  
    EA-I. Roberts: Housing

    lath, or sheathing; steel (thin sheets) coated with a lead-tin alloy; paper,

    laminated with asphaltum, reinforced with cords or fibers, and coated with

    aluminum paint.

            This type of insulation generally provides a vapor barrier in addition to

    its insulation qualities. Dust settling on the reflective surfaces reduces the

    insulation values. It has been found that this type of insulation is most

    effective when installed horizontally and when the flow of heat through the

    insulation is downward. Therefore, this type of insulation is most effective

    when used to keep out summer heat or if used to insulate the floor in winter.

            Insulation Values . The heat conductivity of a material is a measure of

    its insulating value; the lower the conductivity the more effective (see Table I).

    Thermal conductivity, k , is the amount of heat in B.t.u. which will flow in one

    hour through a layer of material one [ ?] square foot in area, where the

    temperature difference between the surfaces of the layer is 1°F. per foot of

    thickness. Thus the insulating value of a layer of material depends upon the

    thickness of the layer as well as the k value of the material. In general, the

    various types and makes of insulation are rated by their ability to resist the

    flow of heat. A resistivity value, r , has been established for the heat resis–

    tance offered by a unit area and unit thickness of each type of insulation material.

    This is equal to the unit thickness of a layer of material divided by the k

    value of the material. The insulating ability of one material may be compared with

    the insulating ability of other insulating materials by comparing their resis–

    tivity values. The larger the r value, the greater the insulating ability.

            When making such comparisons it must be remembered that only the insulating

    materials themselves are being compared and no consideration is being given to

    the effectiveness of the entire installation. After application, the r value

    018      |      Vol_IIA-0433                                                                                                                  
    EA-I. Roberts: Housing

    Table I. Thermal Conductivities and Thermal Resistivities of Building Materials.
    Materials Weight,

    lb./cu.ft.
    Conductivity,

    k
    Resistivity,

    r
    Insulating

    rating
    Flexible insulation
    Animal hair (felt) 12.0 0.26 3.84 Excellent
    Cotton bats 0.875 0.24 4.17 Excellent
    Eel grass in paper 3.40 0.25 4.00 Excellent
    Glass wool bats 1.50 0.27 3.70 Excellent
    Jute fiber bats 6.70 0.25 4.00 Excellent
    Kapok bats 1.00 0.24 4.17 Excellent
    Kimsul bats 1.50 0.27 3.70 Excellent
    Mineral (rock wool) 10.00 0.27 3.70 Excellent
    Peat moss compressed 11.00 0.26 3.84 Excellent
    Wood fiber bats 3.62 0.25 4.00 Excellent
    Loose insulation
    Ceiba fibers 1.90 0.23 4.35 Excellent
    Cork granulated 8.10 0.31 3.22 Excellent
    Redwood bark 3.00 0.31 3.22 Excellent
    Rock wool 10.00 0.27 3.70 Excellent
    Sawdust (various) 12.00 0.41 2.44 Excellent
    Shavings (various) 8.80 0.41 2.44 Excellent
    Vermiculite 6.20 0.32 3.12 Excellent
    Rigid insulation
    Asbestos fibers 48.30 0.29 3.45 Excellent
    Cane fibers 13.50 0.33 3.03 Excellent
    Cork, compressed

    asphalt binder
    14.50 0.32 3.12 Excellent
    Corn stalk fibers 15.00 0.33 3.03 Excellent
    Glass fibers - 0.40 2.50 Excellent
    Wood fibers:
    Exploded 17.90 0.32 3.12 Excellent
    Hard W w ood 15.20 0.32 3.12 Excellent
    Licorice R r oot 16.10 0.34 2.94 Excellent
    Various 15.00 0.33 3.03 Excellent
    Reflective insulation
    Foil with air space

    with heat flow up:
    1 air space - 0.32 3.13 Excellent
    2 air spaces - 0.27 3.70 Excellent
    3 air spaces - 0.17 5.88 Excellent
    Foil with air space

    with heat flow down:
    2 air spaces - 0.10 10.00 Excellent
    3 air spaces - 0.07 14.29 Excellent



    019      |      Vol_IIA-0434                                                                                                                  
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    Table I. Thermal Conductivities and Thermal Resistivities of Building Materials.
    Materials Weight,

    lb./cu.ft.
    Conductivity,

    k
    Resistivity,

    r
    Insulating

    rating
    Other building materials
    Asbestos millboard 60.5 0.84 1.19 Good
    Asphalt roofing 55.0 0.70 1.43 Good
    Brick, masonry (wet) 120.0 ± 5.00 0.20 Fair
    Cement mortar 100.0 12.00 0.08 Poor
    Concrete, typical 142.0 12.60 0.08 Poor
    Concrete, cinder 97.0 4.90 0.22 Fair
    Concrete (1:2:4) 143.0 9.46 0.11 Poor
    Concrete, expanded

    vermiculite aggregate
    20.0 0.68 1.47 Good
    Concrete pumice aggregate

    (mined in California)
    65.0 2.42 0.41 Good
    Gravel, loose dry 106.0 7.50 0.13 Fair
    Ice, fresh-water 57.5 15.10 0.07 Poor
    Limestone 124.0 6.45 0.15 Fair
    Snow, compacted 15.0 + 0 50.0 1.48 0.67 Good
    Soil, dry-packed 94.0 2.60 0.38 Good
    Woods (across grain):
    Balsa 20.0 0.58 1.72 Excellent
    Douglas fir 34.0 0.67 1.49 Good
    Hemlock 22.0 0.73 1.37 Good
    Oak 38.0 1.02 0.98 Good
    White pine 31.2 0.78 1.28 Good
    Yellow pine (short leaf) 36.0 0.91 1.10 Good
    Yellow pine (long leaf) 40.0 0.86 1.16 Good



    020      |      Vol_IIA-0435                                                                                                                  
    EA-I. Roberts: Housing

    of the insulating material is but one factor in the over-all effectiveness of

    the installation. The number of air spaces created, the resistances of the

    various building materials themselves, and the surfaces exposed, all contribute

    to the over-all effectiveness of the insulation provided for the building.

           

    Condensation

            By condensation is meant the moisture which is deposited by the air on the

    inside walls or roof of a building. It does not necessarily occur at all times

    in buildings but is the more rapid the larger the temperature differences,

    especially during periods of relatively high humidity. Air is a mixture of gases

    such as nitrogen, oxygen, etc., and water vapor, all of them normally invisible.

    The gases occur in comparatively fixed relationships but the amount of water

    vapor in air varies greatly. This variation depends on the source of water vapor

    and upon the temperature of the air. Air at higher temperatures can carry more

    water than at lower temperatures.

            Condensation is caused when air, carrying water vapor, is cooled to a

    temperature at which it no longer can carry all of the water which it previously

    contained. This is the dew-point temperature. When the dew point is reached,

    the excess water in the air changes from water vapor to visible liquid or solid

    water. This transition is called condensation.

            Table II gives the maximum weight of water which one pound of air at various

    temperatures can absorb and carry.



    021      |      Vol_IIA-0436                                                                                                                  
    EA-I. Roberts: Housing

    Table II.
    Temperat o u re, °F. Carrying capacity of 1 lb, of air

    in grains* of water
    −50 0.29
    −40 0.55
    −30 1.02
    −20 1.84
    −10 3.22
    0 5.51
    10 9.20
    20 15.06
    30 24.18
    40 36.49
    50 53.61
    60 77.56
    70 110.74
    80 156.31
    90 218.3
    100 302.3
    110 416.1
    120 570.4
    130 781.2
    140 1,073.8
    150 1,487.5 (0.21 lb.)

    * 7,000 grains equal 1 lb.

            The moisture-carrying capacities shown are for the same air pressure so as to run in this para with preceding page

    give comparative figures. Notice that a pound of air can absorb and carry

    110.74 grains of water at 70°F. The same pound of air can absorb less than numbers changed in this paragraph to conform with numbers in table.

    half of this amount at 50°, less than one-fourth at 30°, and less than one-tenth

    (9.20 grains) at 10°F.

            The table gives the maximum amount of moisture that air can carry at the

    temperature shown. When carrying this maximum , the air is called saturated and

    has a relative humidity of 100%. Usually air is not fully sat i u rated with water

    vapor and therefore seldom has a 100% relative humidity. The ratio of the amount

    of water vapor in the air to the amount which it can hold when saturated is called

    022      |      Vol_IIA-0437                                                                                                                  
    EA-I. Roberts: Housing

    the relative humidity. If the relative humidity is 50%, the air contains one–

    half of the water which it can carry when fully saturated at the same temperature.

    Outside air brought into a building and heated will have a drying effect, even

    though rain is falling and the air outside is practically saturated. For when

    saturated air is warmed, it is no longer saturated but becomes capable of carry–

    ing more moisture.

            At this point it is perhaps well to consider the sources of this water vapor.

    Water may exist in three forms. We usually think of it in liquid form. It also

    exists in solid form, which is called ice, or it may exist in a gaseous form,

    which is called water vapor or steam. Steam is invisible; the white cloud

    commonly called “steam” actually is condensed steam and consists of visible

    particles of water.

            With no water vapor in the air, condensation could not take place. One hun–

    dred per cent dry air is difficult to obtain even in a laboratory and such air is

    not desirable from the human living standpoint. All outside air, even that in

    a desert, carries a certain amount of water vapor; the air of warm deserts is

    seldom as deficient in water as that of a fifty-below-zero day of the northern

    winter. During a rainstorm, the outside air is practically saturated. The amount

    of moisture in outside air, therefore, varies greatly depending on the surround–

    ings, the temperature, and the atmospheric conditions.

            In addition to the moisture which is in the outside air, water vapor may be

    liberated inside of buildings from the bodies of the occupants or through other uses

    of the building. Because water vapor is low-pressure steam, any operation such as

    cooking, washing, bathing, or drying clothes adds to the amount of water vapor in

    a building. Potted plants give off moisture. Animals and humans also give off a

    023      |      Vol_IIA-0438                                                                                                                  
    EA-I. Roberts: Housing

    certain amount of moisture, depending upon how fast they use their energy. A man

    at rest liberates 0.2 lb. of water per hour while a man at normal work liberates

    0.6 lb. per hour. A man walking 4 miles per hour liberates 0.9 lb. per hour.

            In addition to the moisture in outside air and moisture from building uses,

    water vapor is also produced by damp surroundings, wet floors, etc. If condensa–

    tion problems persist within any building, it is advisable first to determine if

    the sources of water vapor can be controlled. If these are not subject to regula–

    tion, it becomes necessary to control the water vapor itself.

            Methods of Condensation Control . Condensation may be controlled or entirely prevented in buildings by main–

    taining the inner surfaces at or above dew-point temperatures, or by reducing the

    relative humidity. These two objectives are attained by various methods.

            1. Insulation. From a review of the moisture-carrying capacities of air

    at various temperatures, it is obvious that if interior air does not become

    cooled when it comes in contact with the walls or roof of a building, it will not

    lose its moisture-carrying capacity, so condensation will not occur. This method

    of control requires insulation to keep the inner surfaces of the walls and roof

    near room temperature. In such installations, the moist [ ?] inte r ior air comes in

    contact with the inner surfaces of the insulation and not with things like cold

    metal in walls or roof. Condensation is prevented because the interior surfaces

    of the insulation are near room temperature. Care must be taken to install a

    vapor barrier on the warm side of the insulation, as described below, in order to

    retard the filtering of water vapor through the insulation itself.

            2. Ventilation. It is obvious from the above that condensation will not

    occur if there is no difference in temperature between the inside and the outside

    024      |      Vol_IIA-0439                                                                                                                  
    EA-I. Roberts: Housing

    of a building. This sameness of temperature inside and outside is most easily

    maintained by ventilation, merely by keeping doors, windows, louvers, or venti–

    lators open. However, in certain instances, forced or mechanical ventilation

    may be required. It is obvious that this type of control is a summer method; due

    to the low temperatures involved in an arctic winter this method is not satis–

    factory at that season if warm buildings are required.

            3. Humidity Regulation. Condensation can be controlled by reducing the

    amount of water vapor in the air (relative humidity), since condensation will

    not occur if the amount of water vapor is kept within the air’s ability to carry

    the vapor at the lowest air temperatures. Certain uses of such buildings as

    kitchens, laundries, and bathrooms create a great amount of water vapor as a by–

    product of operation. In such installations, the increasing amount of water vapor

    has a tendency to saturate the air and finally to condense, if not removed. Fre–

    quent changes of interior air are [ ?] recommended to prevent the accumulation of

    these vapors. It is desirable, in certain installations, to remove the excess

    vapor at its source by installing special exhaust ducts. However, the excess can

    be removed in most instances by opening windows, ventilators, louvers, or by the

    use of exhaust fans. By such operation, the cooler outside air enters the build–

    ing; when warmed, it is able to absorb additional moisture. As it leaves the build–

    ing, in its warmed condition, it carries out more water vapor than was brought

    in by the cooler incoming air. In the Subarctic and Arctic, where extreme tempera–

    tures of −50°F. may be expected, the relative humidity may be as high as 80 or

    90%. The actual moisture content of the air at this temperature is slight. Air

    with a temperature of −50°F. if taken into a building and warmed to 70°F., without

    moisture being added, will have a very low relative humidity, possibly less than 5%.



    025      |      Vol_IIA-0440                                                                                                                  
    EA I. Roberts: Housing

            The amount of water vapor in the interior air may also be reduced by dehydrat–

    ing agents such as silica gel, etc., or by mechanical dehydration processes. De–

    hydration by these methods is a relatively expensive procedure.

            4. Vapor Barrier. If the water vapor, which is in the air, is kept from

    coming in contact with the cooler walls and roof, no condensation can occur.

    Keeping the moisture of the interior air from the cold walls and roof is accomplished

    by installing a vapor barrier such as a waterproof membrane or diaphragm between

    the interior air and the walls or roof. Obviously, the vapor barrier must be

    kept at a temperature above the dew point or else the water vapor will condense

    on the barrier itself. It is, therefore, necessary to place the vapor barrier

    on the warm side of the insulation.

            Table III lists the vapor transmission rates of the better-known materials;

    the lowest transmission rates [ ?] how the most effective vapor barriers.



    026      |      Vol_IIA-0441                                                                                                                  
    EA-I. Roberts: Housing

    Table III.
    Materials Transmission of water vapor

    in grains/sq.ft./hr./in. of

    mercury pressure difference
    Double-faced aluminum foils surfaces 0.085 - 0.129
    Roll roofing (smooth surface);
    40# to 65# per 100 sq.ft. roll 0.129 - 0.171
    Asphalt-impregnated sheathing paper:
    50#/500 sq.ft. roll 0.213 - 0.770
    35#/500 sq.ft. roll 0.171 - 2.060
    Insulation back-up paper, treated 0.660 - 3.420
    Gypsum lath with aluminum foil backing 0.085 - 0.385
    Plaster and wood lath 11.000
    Plaster and 3 coats lead and oil paint 3.680 - 3.850
    Plaster and 3 coats flat wall paint 4.280