(2) Soil mixture preparation. Lime should be thor-
treatment is recommended if a 50 percent reduction in
oughly and intimately mixed into the soil to a suffi-
the PI is obtained at the LMO content (table 7- 1). The
cient depth to be effective. For stabilization of expan-
PI should be determined for the natural soil, LMO,
LMO+ 2, and LMO - 2 percent content.
sive clay soils for foundations of structures, mixing
(b) The increase in strength of the lime-treated
should be done down to depths of active zone for
heave. In practice, mixing with lime is rarely done
soil should be similar for soil allowed to cure at least 2
deeper than 1 to 2 feet. Therefore, lime treatment is
or more days following mixing and prior to compaction
normally not useful for foundations on expansive soil
to similar densities.
(c) The amount of lime needed to cause the opti-
except in the above applications. Moreover, poor mix-
mum reduction in the PI usually varies from 2 to 8 per-
ing may cause the soil to break up into clods from nor-
cent of the dry soil weight.
mal exposure to the seasonal wetting/drying cycles.
The overall soil permeability is increased and provides
e. Cement treatment. Cement may be added to the
paths for moisture flow that require rapid drainage
soil to minimize volume changes and to increase the
from this soil. Lime treatment should be performed by
shear strength of the foundation expansive soil if the
experienced personnel.
degree of soil stabilization achieved by lime alone is
(3) Lime modification optimum content (LMO).
not sufficient. The amount of cement required will
The LMO corresponds to the percent of lime that maxi-
probably range between 10 to 20 percent of the dry
mizes the reduction in the soil plasticity or the PI. The
soil weight. A combination of lime-cement or lime-ce-
reduction in plasticity also effectively minimizes the
ment-fly ash may be the best overall additive, but the
volume change behavior from changes in water con-
best combination can only be determined by a labora-
tent and increases the soil shear strength.
tory study. TM 5-822-4 presents details on soil sta-
(a) A decision to use lime should depend on the
bilization with cement and cement-lime combinations.
degree of soil stabilization caused by the lime. Lime
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