TM 5-852-4/AFM 88-19, Chap 4
frozen. Possibly both non-frozen and frozen materials
different types of dynamic loading and different
may be present in a foundation, complicating the
parameters are required. Such properties as module,
problem.
damping ability, and velocity of propagation vary
(1) High stress dynamic loads. While high
significantly with such factors as dynamic stress, strain,
frequency, temperature, and soil type and condition.
stress loads may result from a variety of causes, most
b. Determination of response characteristics of
available design criteria have been developed for the
foundation materials. The testing of frozen materials
case of protection of a structure against the shock
loadings imposed by explosions. Design of the structure,
under dynamic loading has been only recently explored
including the foundation, for stresses resulting from
and relatively few published data are available. Some
18
explosions is covered in TM 5-856-4 . In general, the
data are shown in figure 2-17. It will usually be
necessary to conduct a test program for the particular
pressures resulting from an air blast are more critical to
site and the particular soils involved.
surface facilities than ground transmitted shock waves,
(1) In-situ tests.
Two methods are
and the question of the response of the soil does then
available. In a procedure described in a Waterways
not particularly enter the problem. However, if the
Experiment Station paper a vibrator is placed on the
structure is underground or the shock source is in the
106
surface and operated at a range of frequencies . The
ground, then consideration must be given to the
characteristics of the stress wave propagating through
characteristics of the wave are measured, yielding a
the ground and, in the cold regions, through frozen
relationship between shear modulus and depth. Various
84,124,75
materials. The theory employed and general approach
seismic procedures may also be used
.
to the problem are given in TM 5-856-4. If the stress
(2) Laboratory tests. Few laboratories are
involved is sufficiently low or such that a change in state
presently equipped to test frozen soils under dynamic
of the material does not occur, the required soil
loads, but suitable techniques are available. Foundation
properties may be obtained as discussed in (3) below. If
analysis for high stress, shock type loads requires
a change in-state does occur, as is possible in shock
knowledge of the equation of state for the condition of
type loads, then the pressure-density-temperature
interest so that the conservation of energy laws may be
relationship for the particular material must be
applied.
Test techniques yielding pressure-volume-
obtained32,63,67,90,121,176.
temperature relationships for frozen soils have been
32,63,128,170,176
described in several papers
.
Design
(2) Dynamic
loads
imposed
by
analysis for low stress, steady-state vibration type
earthquakes.
loading requires values for deformation moduli, velocity
(a) TM 5-809-10/AFM 88-3, Chapter
3
of wave propagation, and internal damping for the
13 , presents criteria for design of structures against
68
93
particular soil. Kaplar and Stevens have described
earthquake damage, including earthquake intensities for
design purposes for the state of Alaska and some other
two test techniques. The first of these techniques yields
cold regions locations. Recent suggested procedures for
moduli of elasticity and rigidity, longitudinal and torsional
earthquake design employ response spectrum
velocities of wave propagation, and Poisson's ratio. The
techniques wherein the response of the structure in each
second technique uses viscoelastic theory and yields
mode is considered and total response is obtained by
complex Young's moduli, dilatational and shear velocities
combining the separate modal responses. An example
and internal damping factor expressed as the tangent of
93,94
of the application of this technique has been presented
the lag angle between stress and strain
. The latter
190
by Severn and Taylor .
value may be expressed as an attenuation coefficient.
(Consider a plane wave passing through a solid. If the
(b) All design techniques employed
displacement amplitude at a distance from the source is
for nonfrozen soil conditions are applicable to frozen soil
A19 and at a distance, X1 farther along is A25 then: A2 = A,
conditions, but the response of frozen soils to
e , and α is the attenuation coefficient. It is a property
-ax
earthquake load may obviously be quite different. Of
primary concern is the brittleness, greater stiffness and
of the material.) If damping is small as it usually is in
overall rocklike behavior of frozen soil as compared with
frozen soils, the complex modulus does not differ
nonfrozen soil. Stress wave velocities are much higher
significantly from the elastic modulus.
c. The response of frozen materials to
and damping is generally lower in the frozen soil.
dynamic loads. In general, frozen soils are more brittle,
Propagation of the stress wave through permafrost may
be faster and of higher intensity than for non-frozen soils.
are stiffer (that is, have higher moduli) and have less
(c) The U.S. Geological Survey has
damping capacity than non-frozen soils. However, these
reported observations, on the Alaskan earthquake of
properties vary widely, primarily with temperature, with
201
1964 . Seasonally frozen soil on the surface acted as
ice volume/s oil volume ratio, soil type, load
characteristics, and degrees of ice saturation and
a more or less rigid blanket over the underlying non-
segregation. The classification system for frozen soils
frozen soil. Where the blanket was 2 or 3 feet thick,
describes frozen soils in terms of the most fundamental
cracks of a brittle nature occurred, sometimes forming
of these parameters. Rock also tends to be stiffer when
large slabs of
4-85
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