Environmental Engineering Reference
In-Depth Information
50
16 (Vermiculite)
PI = 122
40
380
01PB
30
FIGURE 10.40
Clay fraction and plasticity index of
natural soils in relation to activity of
natural soils in relation to activity chart of
Skempton, A.W.,
Proceedings of the 3rd
International Conference on Soil Mechanics
and Foundation Engineering,
Zurich, Vol. I,
1953, pp. 57-61. (After Basu, R. and
Arulanandan, K.,
Proceedings of the 3rd
International Conference on Expensive Soils,
Haifa, Israel,
1973.)
9
130
20
15
11
10
7
1
2,12
8
3
0
0
10
20
30
40
50
60
70
Clay fraction (<2
m)%
ยต
TABLE 10.4
Relation of Soil Index Properties to Probable Volume Changes for Highly Plastic Soils
a
Data from Index Tests
b
Colloid Content (%)
Plasticity
Shrinkage
Probable Expansion,
Degree of
<
0.001 mm
Index
Limit (%)
Percent Probable Total
Expansion
Volume Change
(dry to saturated condition)
>
28
>
35
11
>
30
Very high
20-31
25-41
7-12
20-30
High
13-23
15-28
10-16
10-20
Medium
<
15
18
15
<
10
Low
a
From USBR, Earth Manual, U.S. Bureau of Reclamation, Federal Center, Denver, CO, 1974. With permission.
b
All three index tests should be considered in estimating expensive properties.
c
Based on a vertical loading of 1.0 psi as for concrete canal lining. For higher loadings the amount of expan-
sion is reduced, depending on the load and day characteristics.
Prediction from Index Tests
Any surface clay with plasticity index PI
25 (CH clays) and a relatively low natural
moisture content approaching the plastic limit must be considered as having swell poten-
tial. The colloid content (percent minus 0.001 mm), the plasticity index, and shrinkage
limit are used by the USBR (1974) as criteria for estimating the probable total volume
change from the dry to the saturated condition, as given in Table 10.4.
In the method developed by Seed et al. (1962), expansion was measured as percent swell
by placing samples at 100% maximum density and optimum water content in a Standard
AASHO compaction mold under a surcharge of 1psi and then soaking them. A family of
curves given in
Figure 10.41
was developed to describe the percent swell potential for var-
ious clay types in terms of activity and clay fraction present. The chart given in
Figure 10.42
provides another basis for estimating potential expansiveness.
Index tests have limitations. They do not always identify the swell potential for all nat-
ural deposits, nor provide information on the true amount of heave or pressures that may
develop. Because the tests are made on remolded specimens, the natural structure of the
material is destroyed and other environmental factors are ignored.
