TM 5-818-1 / AFM 88-3, Chap. 7
are dependent on such variables as gradation, density,
reduce penetration by increasing the volumetric latent
degree of saturation, ice content, unfrozen moisture
heat of fusion as well as the volumetric specific heat
content, temperature, dissolved soils, and rate of
capacity. While an increase in moisture also increases
loading. Frozen soils characteristically exhibit creep at
thermal conductivity, the effect of latent heat of fusion
stresses as low as 5 to 10 percent of the rupture strength
tends to be predominant. TM 5-852-6/AFM 88-19,
in rapid loading. Typical strength and creep relationships
Chapter 6, contains charts showing thermal conductivity
are described in TM 5-852-4/AFM 88-19, Chapter 4.
relationships.
(2) Ice. Ice that is present in the ground in
e. Frost-heave forces and effect of surcharge.
Frost- heave forces on structures may be quite large.
excess of the normal void space is most obvious as
For some engineering construction, complete prevention
more or less clear lenses, veins or masses easily visible
of frost heave is unnecessary and uneconomical, but for
in cores, and test pits or excavations, but it may also be
most permanent structures, complete prevention is
so uniformly distributed that it is not readily apparent to
essential. Under favorable soil and foundation loading
the unaided eye. In the annual frost zone, excess ice is
conditions, it may be possible to take advantage of the
formed by the common ice segregation process,
effect of surcharge to control heave. It has been
although small amounts of ice may also originate from
demonstrated in laboratory and field experiments that the
filling of shrinkage cracks; ice formations in this zone
rate of frost heaving is decreased by an increase of
disappear each summer. Below the annual frost zone,
loading on the freezing plane and that frost heaving can
excess ice in permafrost may form by the same type of
be completely restrained if sufficient pressure is applied.
ice segregation process as above, may occur as vertical
However, heave forces normal to the freezing plane may
ice wedges formed by a horizontal contraction-expansion
reach more than 10 tons per square foot. Detailed
process, or may be "fossil ice" buried by landslides or
information on frost-heaving pressures and on the effect
other events. Although most common in fine- grained
of surcharge is presented in TM 5-852-4/AFM 88-19,
soils, substantial bodies of excess ice are not uncommon
Chapter 4.
in permanently frozen clean, granular deposits. The
f. Type of structure. The type and uses of a
possible adverse effects of excess ice are discussed in
paragraph 18-4a(2)(b).
structure affect the foundation design in frost areas as in
(3) Rock. Bedrock subject to freezing
other places. Applicable considerations are discussed in
temperatures should never be assumed problem-free in
TM 5-852-4/AFM 88-19, Chapter 4.
absence of positive subsurface information. In seasonal
frost areas, mud seams in bedrock or concentrations of
18-3.
Site investigations.
fines at or near the rock surface, in combination with the
a. General. In addition to the needed site
ability of fissures in the rock to supply large quantities of
investigations and data described in the manuals for
water for ice segregation, frequently cause severe frost
nonfrost conditions, design of foundations in areas of
heave. In permafrost areas, very substantial quantities
significant frost penetration requires special studies and
of ice are often found in bedrock, occurring in fissures
data because of factors introduced by the special frost-
and cracks and along bedding planes.
related site conditions.
Detailed site investigation
d. Water conditions.
procedures applicable for arctic and subarctic areas are
(1) If free water drawn to developing ice
described in TM 5-852-2/AFM 88-19, Chapter 2, and TM
segregation can be easily replenished from an aquifer
5-852-4/AFM 88-19, Chapter 4, and may be adapted or
layer or from a water table within a few feet of the plane
reduced in scope, as appropriate, in areas of less severe
of freezing, heave can be large. However, if a freezing
winter freezing. Methods of terrain evaluation in arctic
soil has no access to free water beyond that contained in
and subarctic regions are given in TM 5-852-8.
voids of the soil immediately at or below the plane of
b. Remote
sensing
and
geophysical
freezing, frost heave will necessarily be limited.
investigations.
These techniques are particularly
(2) In permafrost areas, the supply of
valuable in selection of the specific site location, when a
water available to feed growing ice lenses tends to be
choice is possible. They can give clues to subsurface
limited be- cause of the presence of the underlying
frozen ground conditions because of effects of ground
impermeable permafrost layer, usually at relatively
freezing upon such factors as vegetation, land wastage,
shallow depths, and maximum heave may thus be less
and soil and rock electrical and accoustical properties.
than under otherwise similar conditions in seasonal frost
c. Direct site investigations. The number and
areas. However, uplift forces on structures may be
extent of direct site explorations should be sufficient to
higher because of lower soil temperatures and
reveal in detail the occurrence and extent of frozen
consequent higher effective tangential adfreeze strength
values.
(3) The water content of soil exerts a
substantial effect upon the depth of freeze or thaw
penetration that will occur with a given surface freezing
or thawing index. Higher moisture contents tend to
18-5
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