TM 5-852-1/AFR 88-19, Volume 1
throughout a geographic region, with the exception of
moisture-saturated fine-grained soils on slopes is
widely scattered locations.
reduced during thaw.
(13) Frost-susceptible soil. Soil that will
(29) Permafrost, discontinuous.
experience significant ice segregation when the requisite
frost occurring in some areas beneath the ground
moisture and freezing conditions are present. Such soils
surface throughout a geographic region where other
are further defined in TM 5-818-2/AFM 88-6, Chap. 4.
areas are free of permafrost.
(14) Frost table.
(30) Permafrost table. An irregular surface
The surface, usually
irregular, that represents the level, at any time in spring
within the ground that represents the upper boundary of
and summer, to which thawing of seasonal frozen
(31) Residual thaw layer.
A layer of
ground has penetrated.
(15) Frost thrust. A force due to frost
unfrozen ground between the permafrost and the annual
frost zone. This layer does not exist where annual frost
(16) Frozen zone. A range of depth within
(active layer) extends to permafrost.
The perceptible slow
which the soil is frozen.
(17) Ground ice. A body of more or less
downslope flow of saturated unfrozen soil over a base of
impervious or frozen material. Movement takes place
soil-free ice within frozen ground.
(18) Heterogeneously froze. soil. A soil
primarily when melting of segregated ice or infiltration of
surface runoff concentrates excess water in the surface
with part of its water frozen as macroscopic ice
soil, which then behaves like a viscous fluid.
occupying space in excess of the original voids in the
(33) Suprapermafrost. The entire layer of
(19) Homogeneously frozen soil. A soil in
ground above the permafrost table.
(34) Tangential adfreeze shear. Tangential
which water is frozen within the material voids without
shear between frozen ground or ice and another material
macroscopic segregation of ice.
(20) Ice segregation. The grow the of ice
to which it is bonded by freezing.
(35) Thaw-stable froze soils. Frozen soils
within soil in excess of the amount that would be
that do not, on thawing, show loss of strength below
produced by the in-place conversion of the original void
normal, long-time thawed values nor produce detrimental
moisture to ice. Ice segregation occurs most often as
distinct lenses, layers, veins and masses, commonly, but
(36) Thaw-stable frozen soils. Frozen soils
not always, oriented normal to the direction of heat loss.
(21) Ice wedge. A wedge-shaped ice mass
that show, on thawing, significant loss of strength below
normal, long-time thawed values or significant
in permafrost, usually associated with fissures on trough
settlement, as a direct result of the melting of excess ice
in the soil.
c. Temperature-related terms.
Cohesionless materials such as crushed rock, gravel,
(1) Average annual temperature.
sand, slag and cinders in which there is no significant ice
average of the average daily temperatures for a
segregation under normal freezing conditions (see TM
5818-2/AFM 886. Chap. 4).
(23) Normal period. The time of the year
(2) Average daily temperature.
when there is no alteration in strength of foundation
average of the maximum and minimum temperatures for
materials because of frost action. In seasonal frost
one day or the average of several temperature readings
areas, it generally extends from mid or late spring to mid
taken at equal time intervals during one day, generally
or late fall.
(24) Open system. A condition where free
(3) Average monthly temperature. The
water in excess of that contained originally in the voids of
average of the average daily temperatures for a
the soil is available to be moved to the surface of
(4) Breakup period. The period of the
freezing to form segregated ice in frost-susceptible soil.
(25) Percent heave. The ratio, expressed
spring thaw during which the ground surface is
as a percentage, of the amount of heave to the depth of
excessively wet and soft, and ice is disappearing from
streams and lakes. Duration of the breakup period
(26) Permafrost. Perennially frozen ground.
varies usually from 1 to 6 weeks, depending on region or
local climatic conditions.
It may be defined more specifically as a thermal
(5) Degree-days. The degree-days for
condition in soil or rock in which temperatures below
any one day equal the difference between the average
32F persist over at least two consecutive winters and
daily air temperature and 32F. The degree-days are
the intervening summer.
(27) Permafrost base. The lower boundary
negative when the average daily temperature is below
32F (freezing degree-days) and positive when above
(28) Permafrost, continuous. Permafrost
(thawing degree-days). Degree-days may be computed
in either Fahrenheit or Celsius units; in this
occurring everywhere beneath the exposed land surface