TM 5-852-4 Arctic and Subarctic Construction: Foundations for Structures

269 Pages·1997·4.4 MB·English

ARMY TM 5-852-4
AIR FORCE AFM 88-19, Chap. 4
ARCTIC AND SUBARCTIC
CONSTRUCTION FOUNDATIONS
FOR STRUCTURES
DEPARTMENT OF THE ARMY AND THE AIR FORCE
OCTOBER 1983
TM 5-852-4/AFM 88-19, Chap. 4
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Foundations for Structures, 15 October 1983."
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*TM 5-852-4/AFM 88-19, Chap. 4
Technical Manual HEADQUARTERS
}
No. 5-852-4 DEPARTMENTS OF THE AR MY
AIR FORCE MANUAL AND THE AIR FORCE
No. 88-19, Chapter 4 Washington, DC, 15 October 1983
ARCTIC AND SUBARCTIC CONSTRUCTION
FOUNDATIONS FOR STRUCTURES
Chapter 1. INTRODUCTION Paragraph Page
Purpose and scope................................................................................................................. 1-1 1-1
Environmental conditions in the Arctic and Subarctic.............................................................. 1-2 1-1
2. BASIC CONSIDERATIONS AFFECTING FOUNDATION DESIGN
Thermal effects....................................................................................................................... 2-1 2-1
Seasonal frost heave and settlement...................................................................................... 2-2 2-3
Groundwater........................................................................................................................... 2-3 2-5
Effect of surcharge.................................................................................................................. 2-4 2-8
Foundation materials.............................................................................................................. 2-5 2-11
Structural materials................................................................................................................. 2-6 2-26
3. SITE INVESTIGATIONS
General................................................................................................................................... 3-1 3-1
Remote sensing and geophysical investigation....................................................................... 3-2 3-1
Detailed direct site exploration ................................................................................................ 3-3 3-2
Site technical data................................................................................................................... 3-4 3-3
4. FOUNDATION DESIGN
Selection of foundation type.................................................................................................... 4-1 4-1
Control of heat transfer and degredation................................................................................. 4-2 4-6
Control of movement and distortion from freeze and thaw...................................................... 4-3 4-59
Allowable design stresses on basis of ultimate strength......................................................... 4-4 4-72
Estimation of creep deformation............................................................................................. 4-5 4-77
Dynamic loading..................................................................................................................... 4-6 4-83
Design of footing, rafts and piers............................................................................................ 4-7 4-92
Piling....................................................................................................................................... 4-8 4-109
Grade beams.......................................................................................................................... 4-9 4-144
Walls and retaining structures................................................................................................. 4-10 4-144
Tower foundations.................................................................................................................. 4-11 4-147
Bridge foundations.................................................................................................................. 4-12 4-152
Culverts.................................................................................................................................. 4-13 4-155
Anchorages............................................................................................................................. 4-14 4-156
Foundations for non-heated facilities...................................................................................... 4-15 4-158
Utilidor and pipeline foundations............................................................................................. 4-16 4-160
Connections of utilities to buildings......................................................................................... 4-17 4-160
Drainage around structures..................................................................................................... 4-18 4-160
Stability of slopes during thaw................................................................................................. 4-19 4-164
5. SURVEY DATUM POINTS
Permanent datum points......................................................................................................... 5-1 5-1
Temporary datum points.......................................................................................................... 5-2 5-3
6. CONSTRUCTION CONSIDERATIONS
Effect of construction procedures on design........................................................................... 6-1 6-1
Excavation.............................................................................................................................. 6-2 6-1
Excavation.............................................................................................................................. 6-2 6-1
Embankment and backfill........................................................................................................ 6-3 6-3
Placing concrete under freezing conditions............................................................................. 6-4 6-4
Protection against the environment......................................................................................... 6-5 6-11
7. MONITORING PERFORMANCE
General................................................................................................................................... 7-1 7-1
Inspections.............................................................................................................................. 7-2 7-1
Vertical movement measurement............................................................................................ 7-3 7-1
Temperature sensing.............................................................................................................. 7-4 7-1
Other systems for freeze and thaw monitoring........................................................................ 7-5 7-3
Monitoring groundwater.......................................................................................................... 7-6 7-4
*This manual supersedes TM 5-852-4, October 1954.
i
TM 5-852-4/AFM 88-19, Chap. 4
Appendix A. REFERENCES................................................................................................................................................................. A-1
B. BIBLIOGRAPHY............................................................................................................................................................... B-1
LIST OF TABLES
Table 1-1. Stages of Relative Human Comfort and the Environmental Effects of Atmospheric Cooling............................................. 1-7
2-1. Approximate Coefficients of Linear Thermal Expansion per °C......................................................................................... 2-3
2-2. Specific Gravity and Strength of Wood............................................................................................................................. 2-28
2-3. Moisture Distribution in Cellular Glass after 20 Years Burial in the Annual Frost Zone, Fairbanks, Alaska....................... 2-40
3-1. Example of Settlement Estimate-Location A, figure 3-7.................................................................................................... 3-11
4-1. n-Factors for Freeze and Thaw (Ration of Surface Index to Air Index)............................................................................. 4-8
4-2. Thaw Penetration Beneath a Slab-on-Grade Building Constructed on Permafrost........................................................... 4-17
4-3. Recommended Perimeter Insulation for Various Design Winter Temperatures................................................................ 4-56
4-4. Allowable Design Cohesive Stress for Saturated Frozen Soils in T/ft' on Basis of Ultimate Strength............................... 4-79
4-5. Constants for Equation .................................................................................................................................................... 4-82
4-6. P-wave Velocities in Permafrost....................................................................................................................................... 4-87
4-7. Computation of Temperature Below Top of Permafrost.................................................................................................... 4-101
4-8. Settlement Computations................................................................................................................................................. 4-105
4-9. Stress Distribution Beneath the Uniformly Loaded Area................................................................................................... 4-108
4-10. Settlement Computations................................................................................................................................................. 4-110
6-1. Effect of Temperature of Materials on Temperature of Various Freshly Mixed Concretes................................................ 6-5
6-2. Insulation Requirements for Concrete Walls and for Concrete Slabs and Canal Linings Placed on the Ground............... 6-9
LIST OF FIGURES
Figure 1-1. Meteorological data and ground isotherms, Fort Yukon, Alaska....................................................................................... 1-2
1-2. Freeze or thaw penetration vs mean annual temperature................................................................................................. 1-3
1-3. Typical temperature gradients under permafrost conditions, Kotzebue Air Force Station, Alaska.................................... 1-4
1-4. Typical temperature gradients in the ground..................................................................................................................... 1-5
2-1. Thermal conductivity vs density and porosity of typical materials..................................................................................... 2-2
2-2. Ice wedges in polygonal ground area............................................................................................................................... 2-4
2-3. Moisture content changes caused by freezing.................................................................................................................. 2-6
2-4. Generalization of changing ground conditions as freezing penetrates into the annual frost zone..................................... 2-7
2-5. Plan an delevation of surcharge field experiment, Fairbanks, Alaska............................................................................... 2-7
2-6. Heave vs frost penetration for various applied loadings, surcharge field experiment........................................................ 2-8
2-7. Heave vs frost penetration for various total stresses, surcharge field experiment............................................................ 2-9
2-8. Comparison of laboratory and field measurements of effects of surcharge...................................................................... 2-10
2-9. Maximum frost heave pressures....................................................................................................................................... 2-11
2-10. Summary of maximum stress in compression vs temperature.......................................................................................... 2-14
2-11. Summary of soil characteristics........................................................................................................................................ 2-15
2-12. Summary of maximum stress in tension vs temperature.................................................................................................. 2-18
2-13. Summary of maximum shear stress of frozen soil vs temperature.................................................................................... 2-19
2-14. Effect of rate of stress application on failure strength....................................................................................................... 2-20
2-15. Plastic deformation of frozen soils under constant compressive stress............................................................................ 2-21
2-16. Compressive strength vs ice content, Manchester fine sand............................................................................................ 2-22
2-17. Longitudinal and torsional wave velocity, dynamic moduli of elasticity and rigidity, Poisson's ratio vs temperature.......... 2-23
2-18. Typical record of ice in permafrost.................................................................................................................................... 2-25
2-19. Influence of moisture and temperature on strength of wood............................................................................................. 2-29
2-20. Effect of temperature on strength of wood........................................................................................................................ 2-30
2-21. Toughness shown in flexure test...................................................................................................................................... 2-31
2-22. Effect of temperature on flexure properties and of temperature and moisture content on modulus of elasticity of wood... 2-32
2-23. Effect of concrete mix and moisture conditions on strength of concrete at low temperatures........................................... 2-34
2-24. Moisture absorption of insulation board by soaking in water............................................................................................. 2-36
2-25. Internal moisture distribution in insulation board under different test conditions............................................................... 2-37
3-1. Required extent of explorations for large structure........................................................................................................... 3-3
3-2. Typical exploration log...................................................................................................................................................... 3-6
3-3. Dry density and water content vs depth for a soil exploration in permafrost..................................................................... 3-7
3-4. Thaw-consolidation test on undisturbed sample................................................................................................................3-8
3-5. Consolidation test results for undisturbed samples from two drill holes at same site........................................................ 3-9
3-6. Intergranular pressure vs depth for three explorations at same site................................................................................. 3-10
3-7. Estimated settlement vs depth of thaw for different explorations at the same time........................................................... 3-10
3-8. Pattern of cracks in taxiway pavement, Elmendorf AFB, Alaska....................................................................................... 3-13
3-9. Soil profile, south wall of trench near south edge of taxiway, Elmendorf AFB, Alaska...................................................... 3-14
4-1. Design of foundations in areas of deep frost penetration and permafrost......................................................................... 4-1
4-2. Design alternatives........................................................................................................................................................... 4-2
4-3. Thawing of permafrost under 3 story, reinforced concrete, 500-man barracks, Fairbanks, Alaska................................... 4-3
ii
TM 5-852-4/AFM 88-19, Chap. 4
LIST OF FIGURES CONT.
Figure 4-4. Approximate depth of thaw or freeze vs air thawing or freezing index and n-factor for various homogeneous page
soils.................................................................................................................................................................................. 4-9
4-5. Thaw progression under undisturbed surface, Camp TUTO (near Thule Air Base), Greenland........................................ 4-11
4-6. Thaw vs time, Canadian locations.................................................................................................................................... 4-12
4-7. Depth of thaw vs air thawing index for unpaved surfaces................................................................................................. 4-14
4-8. Thaw depth as affected by runway construction on permafrost........................................................................................ 4-15
4-9. Effect of heated structure size on depth and rate of thaw................................................................................................. 4-16
4-10. Degradation of permafrost under five-story reinforced concrete structure, Fairbanks, Alaska.......................................... 4-18
4-11. Permafrost degradation under 16-ft-square heated test buildings without air space, beginning at end of construction..... 4-19
4-12. Typical foundation thaw near Fairbanks, Alaska............................................................................................................... 4-20
4-13. Typical design for light structure with air space and gravel mat........................................................................................ 4-22
4-14. Foundation in permafrost area for men’s barracks, Thule, Greenland.............................................................................. 4-22
4-15. Post and pad type foundation for composite building, Fort Yukon, Alaska........................................................................ 4-23
4-16. Footing on permafrost foundation, Bethel, Alaska............................................................................................................ 4-24
4-17. Footings on permafrost..................................................................................................................................................... 4-25
4-18. Typical ventilated foundation design for structures supported on piles............................................................................. 4-26
4-19. Wood pile foundation for small residences, Fairbanks, Alaska......................................................................................... 4-27
4-20. Typical pile foundation for light utility building, Fairbanks, Alaska..................................................................................... 4-28
4-21. Steel pile foundation for utility building showing sunshade, Bethel, Alaska....................................................................... 4-29
4-22. Foundation for men’s club, Thule, Greenland................................................................................................................... 4-30
4-23. Two story steel frame building on footings and piers at Churchill, Manitoba, Canada....................................................... 4-31
4-24. Utility and maintenance building, Fairbanks, Alaska......................................................................................................... 4-32
4-25. Ducted foundation for garage, Fairbanks, Alaska............................................................................................................. 4-33
4-26. Pan duct foundation, Thule, Greenland............................................................................................................................ 4-34
4-27. Typical pan duct foundation, showing section at plenum chamber and at interior column for warehouse, Sondrestrom
AB, Greenland.................................................................................................................................................................. 4-35
4-28. Foundation details and maximum thaw penetration for selected years, hangar at Thule, Greenland................................ 4-37
4-29. Schematic of ducted foundation....................................................................................................................................... 4-41
4-30. Properties of dry air at atmospheric pressure................................................................................................................... 4-43
4-31. Flow net, concrete slab on grade, uninsulated.................................................................................................................. 4-47
4-32. Flow net, concrete slab on grade, insulated..................................................................................................................... 4-47
(cid:238)
4-33. Flow net, extrapolated from field measurements, with 1- -in. cellular glass insulation, 36 in. long in vertical position.... 4-48
4-34. Floor temperature 6 in. from wall vs daily average air temperature measured at Loring AFB, Maine............................... 4-49
4-35. Comparison of predicted and measured floor temperatures for a concrete slab on gravel with vertical insulation ........... 4-50
4-36. Thermal resistance vs design winter temperature for, various vertical lengths of insulation for kitchens and mess
halls (from electrical analog analyses).............................................................................................................................. 4-51
4-37. Thermal resistance vs design winter temperatures for two vertical lengths of insulation for barrack buildings
(from electrical analog analyses)...................................................................................................................................... 4-54
4-38. Wood frame residence 32 x 32 ft on rigid concrete raft foundation, Fairbanks, Alaska..................................................... 4-60
4-39. Wood frame residence 32 x 32 ft on wood pile foundation, Fairbanks, Alaska................................................................. 4-62
4-40. Wood frame garage, 32 x 32 on rigid concrete raft foundation, Fairbanks, Alaska........................................................... 4-64
4-41. Vertical movement of 50-ft single span bridge on pile-supported concrete abutments, east-west road near Fair-
banks, Alaska................................................................................................................................................................... 4-65
4-42. Frost action effects........................................................................................................................................................... 4-66
4-43. Average heave vs. time.................................................................................................................................................... 4-67
4-44. Test observations, 1962-63, 8-in. steel pipe pile placed with silt-water slurry in dry-augered hole................................... 4-69
4-45. Test observations 1962-63, creosoted timber pile............................................................................................................ 4-70
4-46. Heave isolation................................................................................................................................................................. 4-72
4-47. Frozen soil creep tests, unconfined compression, Manchester fine sand......................................................................... 4-73
4-48. Variation of ultimate strength ratios with temperature for various rates of loading............................................................ 4-74
4-49. Unconfined compression creep curves for frozen Ottawa sand at 29°F............................................................................ 4-74
4-50. Ultimate strength vs time to failure for Ottawa sand (20-30 mesh) at various temperatures, comparing test data
with computed values....................................................................................................................................................... 4-75
4-51. Mohr's envelopes for frozen sand (Ottawa sand, 20-30 mesh)......................................................................................... 4-76
4-52. Stress and time to failure in creep.................................................................................................................................... 4-78
4-53. Mohr envelopes for frozen soils under moderately rapid loading, from tension and unconfined compression tests.......... 4-80
4-54. Frozen soil creep test on Manchester fine sand, unconfined compression, 200 psi at 15 °F............................................ 4-84
(cid:131)
4-55. Frozen soil creep tests on Manchester fine sand, unconfined compression, 15 F........................................................... 4-84
4-56. Complex dynamic Young's modulus vs volume ice/volume soil ratio for frozen saturated, non-plastic soils..................... 4-88
4-57. Complex dynamic shear modulus vs ice saturation.......................................................................................................... 4-89
4-58. Complex dynamic Young's modulus vs ice saturation...................................................................................................... 4-90
4-59. Complex dynamic shear modulus vs dynamic stress at constant frequency (500 Hz), temperature 15 °F........................ 4-91
iii
TM 5-852-4/AFM 88-19, Chap. 4
LIST OF FIGURES CONT.
page
Figure 4-60. Complex dynamic shear modulus vs frequency at constant dynamic stress (1.0 psi), temperature 15 °F........................ 4-91
4-61. Bearing capacity formulas................................................................................................................................................ 4-93
4-62. Boring log and soils condition........................................................................................................................................... 4-96
4-63. Case of isolated square footing........................................................................................................................................ 4-97
4-64. Vertical stress at centerline.............................................................................................................................................. 4-99
4-65. Temperature distribution for permafrost below footing...................................................................................................... 4-101
4-66. Conditions for creep analysis........................................................................................................................................... 4-104
4-67. Unconfined compression creep test - data for Zone B...................................................................................................... 4-106
4-68. Conditions for bearing capacity analysis of square raft..................................................................................................... 4-107
4-69. Frozen soil - diagrams of temperature and stress distribution ........................................................................................ 4-109
4-70. Latent heat of slurry backfill.............................................................................................................................................. 4-115
4-71. General solution of slurry freezeback rate........................................................................................................................ 4-117
4-72. Specific solution of slurry freezeback rate........................................................................................................................ 4-118
4-73. Natural freezeback of piles in permafrost during winter and summer............................................................................... 4-119
4-74. Compressor for artificial freezeback of piles..................................................................................................................... 4-120
4-75. Refrigeration coils on timber piles for artificial freezeback................................................................................................ 4-121
4-76. Influence of slurry on temperature of permafrost between piles........................................................................................ 4-123
4-77. Stresses acting on piling for typical permafrost condition................................................................................................. 4-128
4-78. Response of frozen silt to loading conditions in unconfined compression......................................................................... 4-130
4-79. Load, strain and stress distribution for pile in permafrost with zero load at tip.................................................................. 4-130
4-80. Load test of steel pipe pile................................................................................................................................................ 4-132
4-81. Load distribution along pile during test, strain-gage instrumented pile.............................................................................. 4-133
4-82. Tangential adfreeze bond strengths vs temperature for silt-water slurried 8.625-in.-O.D. steel pipe piles in perma-
frost averaged over 18 to 21 ft embedded lengths in permafrost...................................................................................... 4-134
4-83. Example of computation of sustainable load capacity of pile in permafrost...................................................................... 4-136
4-84. Load-settlement test, 10-kip increments........................................................................................................................... 4-141
4-85. Effect of rate of loading and temperature on adfreeze strength of steel pipe piles............................................................ 4-142
4-86. Load settlement test, single increment............................................................................................................................. 4-143
4-87. Walls and abutments........................................................................................................................................................ 4-145
4-88. Thickness of non-frost-susceptible backfill behind concrete walls.................................................................................... 4-146
4-89. Granular pad tower foundations....................................................................................................................................... 4-148
4-90. Foundation designs employing minimum or no NFS granular borrowed material............................................................. 4-149
4-91. Effects of granular mats on frost penetration and heave................................................................................................... 4-150
4-92. Geologic sections at two Alaska railroad bridges in Goldstream Valley near Fairbanks, Alaska....................................... 4-153
4-93. Mechanics of anchor failure in frozen soils....................................................................................................................... 4-157
4-94. Failure planes for batter and vertical anchor installation................................................................................................... 4-157
4-95. Typical foundation design for unheated buildings over frost-susceptible soil in deep seasonal frost or permafrost areas 4-159
4-96. Exterior apron design....................................................................................................................................................... 4-161
4-97. Utility connections to buildings......................................................................................................................................... 4-162
4-98. Slopes in frost and permafrost areas................................................................................................................................ 4-165
4-99. Ice exposed in vertical cut for Trans-Alaska Pipeline Access Road between Livengood and the Yukon River,
Alaska, April 1970............................................................................................................................................................ 4-167
4-100. Slope resulting from melting of ice in vertical cut face during one summer, Trans-Alaska Pipeline Access Road
between Livengood and the Yukon River, Alaska, August 1970....................................................................................... 4-168
5-1. Recommended permanent benchmark............................................................................................................................. 5-2
7-1. Permafrost and frost probing techniques.......................................................................................................................... 4-4
7-2. Electrical resistance gage for determination of frost penetration...................................................................................... 7-6
iv
TM 5-852-4/AFM 88-19, Chap. 4
CHAPTER 1
INTRODUCTION
1-1. Purpose and scope. (1) In general, mean annual temperatures
a. This manual provides criteria and guidance decrease with increasing latitude or elevation, and the
for design of foundations for structures for military amplitude of the annual air temperature cycle generally
facilities in arctic and subarctic regions. decreases as large bodies of water or oceans are
b. To facilitate the use of this manual, approached. Under natural conditions, mean annual
superscript numbers are used to refer to Appendix A- ground temperatures are usually 2 °F to 5 °F higher than
References. These references have been divided into mean annual air temperatures, though deviations are
publications required to use the manual (Required sometimes outside this range. The difference between
Publications) and additional related publications (Related air and ground temperatures is attributable primarily to
Publications.) additional heat input from absorption of solar radiation at
the ground surface in the summer, to restriction of heat
1-2. Environmental conditions in the Arctic and loss by the insulating effect of a snow cover during the
Subarctic. winter months, and to the normal temperature difference
The design, construction and maintenance of which occurs in heat flow across a solid/gas interface.
foundations are all affected by the special environmental Mean annual air temperatures in the Northern
conditions found in the Arctic and Subarctic 109, 110. Hemisphere are shown in TM 5-852-1'°.
(Superscript numbers indicate references listed in app (2) Air temperatures in arctic
A.) These conditions typically include the following, as environments may range from highs of 75 (cid:131)F to 85 °F in
applicable: the summer to lows of -50°F to -75 °F during the coldest
winter months. It is not uncommon for air temperatures
Seasonal freezing and thawing of to remain below -30°F for a week or more at many
ground with attendant frost heaving and locations in Alaska and in fact air temperatures have
other effects. remained below -50°F for as much as several weeks. A
Occurrence of permanently frozen typical record of air temperatures for a one-year period at
ground subject to thawing and Fort Yukon is shown in figure 1-1, along with other data,
subsidence during and following including ground temperatures.
construction. b. Front conditions.
Special physical behavior and properties (1). Seasonal frost areas are those areas
of frozen soil, rock, and construction where significant freezing occurs during the winter
materials at low temperatures and under season but without development of permafrost. In North
freeze-thaw action. America significant seasonal frost occurs about I year in
Difficulty of excavating and handling 10 in northern Texas. A little farther to the north it is
frozen ground. experienced every year. As indicated in figure 1-2, depth
Poor drainage and possible excess of of seasonal freezing increases northward with
water during thaw caused by the decreasing mean annual air temperature until permafrost
presence of impervious frozen ground at is encountered. With still further decrease of mean
shallow depths. annual temperature, the zone subject to annual freezing
Thermal stresses and cracking. and thawing becomes progressively thinner 164
Ice uplift and thrust action. (2) Permafrost areas174 are those in which
Limited availability of natural perennially frozen ground is found. In North America
construction materials, support facilities, permafrost is found principally north of latitudes 55° to
and labor. 65(cid:131), although patches of permafrost are found much
Adverse conditions of temperature, farther south on mountains where the temperature
wind, precipitation, distance, conditions are sufficiently low, including some mountains
accessibility, working seasons, and cost. in the United States. The depth to the surface of
While these factors are important in many other types of permafrost is dependent primarily on the magnitude of
construction such as pavements6 and utilities3, they merit the air thawing index, the radiational input to the surface
separate consideration for foundations for structures. (as controlled by such factors as latitude, amount of
a. Temperature. The single most important cloudiness, degree of shading or exposure, vegetation,
factor contributing to the existence of these adverse and surface color), and the water content and dry unit
conditions in the northern regions is the prevailing low air weight of the soil.
temperatures, demonstrated not only in the intensity and (a) In zones of continuous
duration of cold in winter itself but also in the low mean permafrost, frozen
annual temperatures.
1-1
TM 5-852-4/AFM 88-19, Chap. 4
U. S. Army Corps of Engineers
Figure 1-1. Meteorological data and ground isotherms, Fort Yukon, Alaska99
1-2
TM 5-852-4/AFM 88-19, Chap. 4
(a) For bituminous paved areas over well drained grovel, kept clear of snow.
(b) a (c) Typical for other soil, moisture and surface conditions.
U. S. Army Corps of Engineers
Figure 1-2. Freeze or thaw penetration vs mean annual temperature 164.
ground is absent only at a few widely scattered locations, time behind the air temperature variations occurring at
as at the bottom of lakes and rivers. the surface 197. The decrease of annual amplitude with
(b) In zones of discontinuous depth is illustrated in a more general way in figure 1-4.
permafrost, permafrost is found intermittently in various Below a depth in the range of 30 to 60 feet, the
degrees. There may be discontinuities in both horizontal amplitude of annual temperature variation becomes
and vertical extents. small and the temperature gradient corresponding to the
(c) The boundaries between zones of normal flow of heat outward from the interior of the earth
continuous permafrost, discontinuous permafrost, and becomes discernible. When the ground temperature
seasonal frost without permafrost are poorly defined. curve with depth at its warmest extreme is below
Distinctions between continuous and discontinuous freezing over a portion of its length, as in figure 1-4, a
permafrost, in particular, are somewhat arbitrary. permafrost condition exists. When the curve shows
(d) Definitions of specialized terms, ground temperatures entirely above freezing at its
more detailed discussions on seasonal frost and warmest extreme, but freezing does occur at its coldest
permafrost, and the approximate extent of continuous extreme, only seasonal frost conditions exist. A
and discontinuous permafrost in the Northern seasonal freeze and thaw zone, called the "annual frost
Hemisphere are given in TM 5-852-1 0 general zone," occurs even in the permafrost areas, except at
provisions. very extreme locations where the air temperatures
c. Thermal regime in the ground. As shown in remain well below freezing even in the summer. The
figure 1-3, temperatures below the ground surface vary annual frost zone is usually not more than 10 feet thick,
with the seasons. The annual ground temperature but it may exceed 20 feet.
fluctuation decreases in amplitude with depth and lags in
1-3
TM 5-852-4/AFM 88-19, Chap. 4
U. S. Army Corps of Engineers
Figure 1-3. Typical temperature gradients under permafrost conditions, Kotzebue Air Force Station, Alaska.
1-4