TM 5-822-14/AFJMAN 32-1019
use of small quantities of lime for soil modification
under some circumstances may result in a frost
susceptible material that in turn can produce a
weak sublayer.
One increment of lime is applied for complete
stabilization to a depth of 18 inches. Mechanical
mixers are now available to pulverize the lime-
clay soil to the full depth by progressive cuts as
follows: first-pass cut to a depth of 6 inches, second
to 9 inches, third to 12 inches, fourth to 15 inches,
and then a few passes to a depth of 18 inches to
accomplish full pulverization. The full 18 inches is
compacted from the top by vibratory and conven-
tional heavy rollers.
Figure 4-21. Lime-cement-fly ash aggregate base course.
(2) Plant mixing. The plant-mix operation usu-
ally involves hauling the soil to a central plant
where lime, soil, and water are uniformly mixed
and then transported to the construction site for
further manipulation (fig 4-20 through fig 4-22).
The amount of lime for either method is usually
predetermined by test procedures. Specifications
may be written to specify the actual strength gain
required to upgrade the stabilized soil, and nota-
tions can be made on the plans concerning the
estimated percent of lime required. This note
should also stipulate that changes in lime content
may be necessary to meet changing soil conditions
encountered during construction.
(3) Pressure injection. Pressure injections of
Figure 4-22. Enclosed soil holds lime for adding to
lime slurry to depths of 7 to 10 feet, for control of
marginal crushed stone base material.
swelling and unstable soils on highways (fig 4-23)
and under building sites, are usually placed on
5-foot spacings, and attempts are made to place
horizontal seams of lime slurry at 8- to 12-inch
intervals. The top 6- to 12-inch layer should be
completely stabilized by conventional methods.
b. Construction steps.
Figure 4-23. Lime slurry pressure injection (LSPI) rig
treating a failed highway slope.
(1) Soil preparation. The in-place subgrade soil
should be brought to final grade and alignment.
The finished grade elevation may require some
adjustment because of the potential fluff action of
the lime-stabilized layer resulting from the fact
that some soils tend to increase in volume when
Figure 4-20. Lime-treated gravel with lime fed by
mixed with lime and water. This volume change
screw conveyor.
4-12
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