TM 5-818-7
strength tests should be performed to characterize the
pressure that must be applied to the soil to reduce the
soil profiles. Swell tests may not be necessary on speci-
volume expansion down to the (approximated) in situ
mens taken at depths below permanent deep ground-
water levels.
in appendix VIII of EM 1110-2-1906 tend to provide
(1) The representative mean of the swell and
lower limits of the in situ swell pressure, while the
strength parameters (and lower limit of the scatter in
simple swell test, figure 4-2, tends to provide upper
strength parameters) of each distinctive soil stratum
limits. The maximum past pressure is often a useful
should be determined down to depths of 1.5 times the
minimum width of mat slabs to a maximum of 100
(2) Soil suction. Soil suction is a quantity that also
feet and to at least three base diameters beneath the
can be used to characterize the effect of moisture on
base of shaft foundations.
volume changes and, therefore, to determine the
(2) One consolidometer swell and one strength
anticipated foundation soil heave. The suction is a ten-
test should be performed on specimens from at least
sile stress exerted on the soil water by the soil mass
five undisturbed samples at different depths within
that pulls the mass together and thus contributes to
the depth of the anticipated active zone (e.g., within 10
the apparent cohesion and undrained shear strength of
to 20 feet beneath the base of the foundation). Suction
the soil. The thermocouple psychrometer and filter
tests may also be performed at relatively frequent
paper methods, two of the simplest approaches for
depth intervals (e.g., l-foot increments) to better char-
evaluation of soil suction and characterization of swell-
acterize swell behavior and thereby increase confi-
ing behavior, are described in appendix B. The suction
dence in prediction of potential heave discussed in
procedure, which is analogous to the procedure for
chapter 5.
characterization of swell from consolidometer swell
(3) One consolidometer swell and one strength
tests, is relatively fast, and the results can increase
test should be performed on specimens from each
confidence in characterization of swell behavior.
undisturbed sample (or at intervals of 2.5 feet. for
continuous sampling) at depths above the base of deep
b. Strength tests. The results of strength tests are
shaft foundations to permit evaluation of the adjacent
used to estimate the soil bearing capacity and load/de-
soil heave and uplift forces exerted on the shaft/soil
flection behavior of shaft or other foundations. The
interface, Suction tests may also be performed to fur-
critical time for bearing capacity in many cases is
ther characterize swell behavior and increase confi-
immediately after completion of construction (first
dence in prediction of potential heave.
loading) and prior to any significant soil consolidation
(4) Suction test results can characterize the pore
under the loads carried by the foundation. The long-
pressure profile by indicating depths of desiccation
term bearing capacity may also be critical in expansive
and wetting, which are useful for minimizing potential
foundation soils because of reductions in strength
foundation problems from soil movement and for eval-
from wetting of the soil.
uating remedial measures to correct problems.
c. Application. Sufficient numbers of swell and
4-5
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