TM 5-852-4/AFM 88-19, Chap. 4
of different soil types but also because variations in
into account in the limited subgrade frost penetration
6
method of pavement design (see TM 5-818-2 ). This
climatic and groundwater conditions may also be
approach to limiting differential movements due to frost
expected to affect the field behavior.
f.
In laboratory freezing experiments, heaving
heaving is also applicable to unheated warehouses, POL
facilities and transmission towers, and may enter into the
pressures of the magnitudes shown in figure 2-9 have
design of many other types of facilities.
been measured under conditions of essentially complete
restraint.
Therefore, if foundation loadings at the
freezing plane equal or exceed these pressures, heave
2-5. Foundation materials.
will be prevented completely. For many engineering
a. Soils.
structures such as pavements, such complete prevention
(1) Permafrost soils cover the entire range
is unnecessary and uneconomical.
For structures
from very coarse, bouldery glacial drift through gravels,
particularly sensitive to movement, however, complete
sands, silts and clays to organic soils.
Slightly
prevention may be essential, and in some cases it may
undersaturated coarse, bouldery frozen soils at low
be feasible to achieve this result by providing sufficient
temperature, such as are encountered in northern
foundation loading, allowable foundation bearing values
Greenland, behave in excavation and tunneling as if they
24
permitting. However, uplift computations cannot be
are granite . At the other extreme, in fat clays at
made simply by applying the pressures of figure 2-9 to
temperatures not far below the freezing point, only a
the areas of direct foundation loading, as frost heave
relatively small percentage of the soil water may actually
uplift acts on the base of a frozen slab of soil whose
be frozen, and the behavior of such soil may be only
effective area may be much greater than the area of the
slightly altered by the freezing temperatures. In some
structure foundation, as illustrated in figure 4-42a. The
heave-reducing effect of surcharge is presently taken
U. S. Army Corps of Engineers
Figure 2-9a. Maximum Frost Heave Pressures. (Pressure and Heave vs Permeability.)
2-11
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