CHAPTER 4
LABORATORY INVESTIGATIONS
4-1. Identification of swelling soils
were performed on 20 undisturbed clays and clay
shales from the states of Mississippi, Louisiana, Texas,
Soils susceptible to swelling can be identified by classi-
Oklahoma, Arizona, Utah, Kansas, Colorado, Wyo-
fication tests. These identification procedures were de-
ming, Montana, and South Dakota. Results of these
veloped by correlations of classification test results
tests for a change in moisture from natural water con-
with results of one-dimensional swell tests performed
tent to saturation at the estimated in situ overburden
in consolidometers on undisturbed and compacted soil
pressure (pressures corresponding to depths from 1 to
specimens. Classification data most useful for identi-
8 feet) indicated the degrees of expansion and poten-
fying the relative swell potential include the liquid
limit (LL), the plasticity index (PI), the COLE (para
sents the percent increase in the vertical dimension or
the percent potential vertical heave. The classification
chemical tests. Several of the more simple and success-
may be used without knowing the natural soil suction,
ful methods recommended for identifying swelling soil
but the accuracy and conservatism of the system are
from classification tests described below were devel-
reduced. Soils that rate low may not require further
oped from selected soils and locations combined with
swell tests, particularly if the LL is less than 40 per-
the results of limited field observations of heave.
cent and the PI is less than 15 percent. Soils with these
These procedures assume certain environmental condi-
Atterberg limits or less are essentially nonexpansive.
tions for surcharge pressure (e.g., 1 pound per square
However, swell tests may be required for soils of low
inch) and changes in moisture from the initial water
swelling potential if the foundation of the structure is
content (e.g., to saturation or zero final pore water
required to maintain small differential movements
pressure),
less than 1 inch (para 4-2c).
a. WES classification. Consolidometer swell tests
c. Van Der Merwe method. This method evolved
b. Texas Department of Highways and Public
from empirical relationships between the degree of ex-
Transportation (TDHPT) method. This procedure,
pansion, the PI, the percent clay fraction, and the sur-
which is known as Tex-124-E of the TDHPT Manual
charge pressure, The total heave at the ground surface
of Testing Procedures, is based on the swell test results
is found from
of compacted soils from Texas. Field heaves of each
--
soil stratum in the profile are estimated from a family
of curves using the LL, PI, surcharge pressure on the
soil stratum, and initial water content. The initial wa-
where
ter content is compared with maximum (0.47 LL + 2)
AH =
and minimum (0.2 LL + 9) water contents to evaluate
D=
the percent volumetric change. The potential vertical
rise (PVR) of each stratum is found from a chart using
the percent volumetric change and the unit load bear-
ing on the stratum. These PVRs for depths of as much
PE =
as 30 feet or more are summed to evaluate the total
PVR. This method may overestimate the heave of low
plasticity soils and underestimate the heave of high
plasticity soils.
and 1 inch/foot for low, medium, high, and very high
.
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