TM 5-852-4/AFM 88-19, Chap. 4
curve directly, i.e., at 1 hour; see figure 4-55 for details.
The foundation soil temperature is nearly constant and is
the same for the model as for the foundation during the
critical period of the year (defined above). The test is
performed in in-situ soil that the structure foundation is to
be founded on and that the same soil conditions extend
at least to a depth equal to the smaller dimension of the
entire foundation. The model dimensions are large
enough to minimize the edge and side effects.
k. The various test requirements may make
this approach difficult to employ; the soil temperature
requirements, for example, may substantially restrict the
time of year within which the field tests may be
performed.
I.
It must be emphasized that the methods
and ideas presented here for predicting creep of frozen
soils are still under investigation.
m. Where the tolerable foundation movement
is very small, a special investigation for the determination
of creep deformation may be required.
An illustration of the use of this method is given in
4-6. Dynamic loading.
paragraph 4-7b(2).
a. General.
h. The third and probably most accurate
(1) Foundations supported on frozen
method of predicting creep is to run a field test on a
ground, ice or snow may be affected by high stress type
prototype or large size model of the foundation under
dynamic loadings such as shock loadings from high yield
consideration and apply equation 6. The field test should
explosions, by lower stress pulse type loadings as from
be performed on the model using the same
earthquakes or impacts, or by relatively low stress,
configuration, soil pressure and soil temperatures as for
relatively low frequency, steady-state vibrations. In
the foundation to be constructed, and on the same
general, the same design procedures used for non-
frozen soil. The design stress should be applied to the
frozen soil conditions are applicable to frozen soils.
model as nearly instantaneously as possible but without
Design criteria are given in TM 5-809-10/AFM 88-3,
impact. (One method of applying the load is to release
3
18
20
Chapter 13 , TM 5-856-4 , and EM 1110-345-310 .
the hydraulic pressure from jacks in a manner so as to
These manuals also contain references to sources of
quickly transfer a dead weight load from the jacks to the
data on the general behavior and properties of non-
model foundation.) After the full load is applied, the
frozen soils under dynamic load and discuss types of
deformation of the model should be recorded at frequent
laboratory and field tests available. However, design
intervals to define the time vs. deformation curve for a
criteria, test techniques and methods of analysis are not
period of eight hours. The elevation should be recorded
yet firmly established for engineering problems of
before loading and immediately after loading. (The
dynamic loading of foundations.
Therefore, HQDA
difference between these two readings gives an estimate
(DAEN-ECE-G), WASH DC 20314 or HQUSAF/PREE,
of the instantaneous deformation that occurs during load,
WASH, DC should be notified upon initiation of design
i.e. eo.) Using the time after load application as time
and should participate in establishing criteria and
zero, then deformation readings should be taken at times
approach and in planning field and/or laboratory tests.
1, 2, 3, 4, 5, 10, 20, 30 minutes, 1 hour, and every hour,
(2) All
design
approaches
require
until 8 hours have elapsed.
knowledge of the response characteristics of the
i.
Using the data obtained from the model
foundation materials, frozen or non-frozen, under the
tests, the values of e, and M in equation 6 can be
particular load involved. As dynamic loadings occur in a
determined graphically. One technique is to use the
range of stresses, frequencies and types (shock, pulse,
slopes of the tangents to the deformation vs. time curve
steady-state vibrations, etc.) and the response of the soil
on arithmetic coordinates at times of 1/2 hour and 1 hour
varies depending upon the load characteristics, the
after stress application (see figure 4-54) for details). A
required data must be obtained from tests that produce
second technique is to determine the rate of deformation
the same responses as the actual load. Different design
of the foundation at several times and plot log e vs. log l/t
criteria are used for the
curve for the 8 hours of the test. The slope of this curve
is the value of M. The value of ε1 can be read from the
4-83
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