UFC 3-260-02
30 June 2001
Table 7-1
Minimum Unconfined Compressive Strength for Cement, Lime, Lime-Cement, and Lime-
Cement-Fly Ash Stabilized Soils
Minimum Unconfined Compressive Strength, psi1
Stabilized Soil Layer
Flexible Pavement
Rigid Pavement
Base course
750
500
Subbase course, select material
250
200
or subgrade
1
Unconfined compressive strength determined at 7 days for cement stabilization and 28 days for lime,
lime fly ash, or lime-cement-fly ash stabilization.
are usually made on soaked remolded samples; however, where existing similar construction is
available, CBR tests should be made in-place on material when it has attained its maximum expected
water content or on undisturbed soaked samples. The procedures for selecting test values described for
subgrades apply to select materials and subbases. Experience has shown that CBR tests on gravelly
materials in the laboratory have tended to give CBR values higher than those obtained in tests in the
field. The difference is attributed to the processing necessary to test the sample in the 152-millimeter
(6-inch) mold, and to the confining effect of the mold. Therefore, the CBR test is supplemented by
gradation and Atterberg limits requirements for subbases, as shown in Table 7-2. Suggested limits for
select materials are also indicated. In addition to these requirements, the laboratory CBR must be equal
to or higher than the CBR assigned to the material for design purposes.
Table 7-2
Gradation and Atterberg Limit Requirements for Subbases and Select Materials
Maximum Permissible Value1
Gradation Requirements
Maximum1
Percent Passing
Design
2.0 mm
.075 mm
CBR
Size, mm (in.)
(No. 10)
(No. 200)
LL
PI
Material
Subbase
50
75 (3)
50
15
25
5
Subbase
40
75 (3)
80
15
25
5
Subbase
30
75 (3)
100
15
25
5
75 (3)2
252
352
122
Select material
20
--
Note:
LL signifies liquid limit; PI signifies plasticity index.
1
EI 02C202/AFJMAN 32-1016 contains maximum values for open graded and rapid draining
materials.
2
Suggested limits.
7-2
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