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