TM 5-852-4/AFM 88-19, Chap. 4
frozen soil. In some cases a pumping action resulted,
Testing to date has not established definitive
wherein non-frozen soil and debris were ejected through
relationships with these variables but data indicating
the cracks in the frozen soil layer. There was mention, in
general trends are available.
(c) Measurements of velocity of the
a few oases, of sliding occurring along the interface of
the frozen and non-frozen layers.
dilatational wave have been made using seismic
(d) The design engineer should
methods. Table 4-6 lists velocities for a variety of frozen
visualize the possible effects of an earthquake on the
soils and rocks. If Poisson's ratio is known or assumed,
foundation, whether it may involve sliding of slabs of
Young's modulus may be calculated from such velocities
frozen soil in winter, sliding of saturated thawed soil over
as follows:
permafrost in summer, or other effect and should avoid
( 1 + ν ) ( 1 2ν ) ρ (Equation 7)
V 2
any situations or actions which may be hazardous or
E= c
1-ν
imprudent.
(3) Low stress, vibratory loads.
Vc =P-wave velocity
where:
(a) Design of foundations for radar
ν = Poisson's ratio
towers with rotating antennas and structures supporting
ρ = mass density
heavy machinery, turbines, generators, and the like,
(d) As the seismic method uses
must consider the response of the foundation and soil
very high rise times, modules values must be
mass to the vibration. Evaluation of natural foundation
considered as upper limits.
frequency, displacements and settlement may be
(e) Figure 2-17 shows dynamic
required. The critical situation may be a condition of
moduli and Poisson's ratio determined by Kaplar for
which
can
produce
unacceptable
various frozen soils at various temperatures". It will be
displacements and settlements and/or interfere with the
noted that the stiffness decreases drastically as
operation of the facility. EM 1110-345-3102o gives a
temperature rises and approaches 32 F. The test
design procedure for predicting the resonant frequency
procedure used in this case did not allow measurement
and displacement under vibratory loads. Three modes of
of internal damping as a material property. No variation
motion are treated: vertical movement, rotation about a
of modulus and velocity with frequency or stress level
vertical axis, and rocking about a horizontal axis. The
was determined and test frequencies ranged from 830 to
equations are based on the elastic half-space concept.
4000 Hz. Stress levels were unknown but were low,
Damping is that involved in dissipation of energy with
such as to give a linear response.
distance; damping as a result of the viscous or internal
(f) The decrease in stiffness with
friction properties of the material is not accounted for.
rising temperature emphasizes the possibility that energy
However, as internal damping is small for many soils,
dissipation into the soil may raise the temperature
especially frozen soils, the procedure is adequate for
sufficiently to alter the foundation response or even its
most cases. A value for the shear modulus of the soil is
stability. A pile embedded in frozen soil and depending
required. Young's modulus and Poisson's ratio may also
for its bearing capacity on the adhesive strength between
be used. The elastic half-space method assumes that
the soil and pile may, under steady-state prolonged
the soil mass is more-or-less homogeneous and
vibration, dissipate energy into the soil sufficiently to
isotropic. If the soil mass radically departs from the
raise the temperature. The state-of-the-art does not
condition, as in the case of a strongly layered soil, a
currently allow calculation of energy dissipation into the
partially frozen condition or similar situation, special
soil and temperature rise at the soil/pile interface under a
design procedures must be employed. Computer codes
given dynamic load. However, the designer should
for calculation are available and two dimensional
consider the possibility.
computer codes are in the state-of-the-art. However, the
(g) Figures 4-56 through 4-60
required properties of the soils are not always directly
illustrate the effect of ice volume/soil volume ratio,
available from test. This is especially true of frozen soils.
degree of ice saturation, frequency and stress on the
Most material property inputs are based on one
modulus. Complete data including the complex Young's
dimensional plane strain tests. It is seldom possible to
and shear moduli, the corresponding velocity of wave
exactly reproduce in tests the complex stress and
propagation, Poisson's ratio, damping expressed as the
deformation states which govern actual behavior under
tangent of the lag angle between stress and strain, and
dynamic loads. Therefore, engineering judgment based
the attenuation coefficient have been reported by
on broad experience and knowledge must be employed
176
CRREL .
in choosing test procedures and in analyzing test results
to select suitable values for use in computer solutions.
(b) The response of frozen soils to
vibratory loads varies with the stress, strain, and
frequency imposed by the load, with exterior influences
such as temperature and confining pressure, and with
the soil characteristics such as void ratio, ice volume/soil
volume ratio, degree of ice saturation and soil type.
4-86
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