an engineering geological characterisation of tropical clays - GBV

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The black clays exhibit significant swelling pressures of 49-104 kPa (Table 7.19). However,
no well defined relationship was found to occur between swelling pressure determined on
undisturbed specimens on one hand; and index properties as well as smectite content of the
clays, on the other. Attempted correlations are generally poor and of low strength (R< 0,6) as
shown in Table (7.19); and evidenced by more spread out plot points on scatter diagrams
(Figures 7.29, 7.30, 7.31, 7.32 & 7.33). This shows the unreliability with which swelling
characteristics of the clays could be estimated and / or predicted from results of index tests.
Black clays
Black clays
Swelling pressure SP (kPa)
120
100
80
60
40
20
n=7
LL vs SP
Swelling pressure SP (kPa)
120
100
80
60
40
20
n=7
PI vs SP
0
0
75 80 85 90 95
30 40 50 60
Liquid limit LL (%)
Plasticity index PI (%)
Figure 7.29. Correlation between LL and SP.
Figure 7.30. Correlation between PI and SP.
Once again therefore, serious uncertainties would still be encountered in attempting to assess
the possible magnitude of swelling pressures of the clay soils in situ based on results of index
tests performed on disturbed and fractioned soil samples.
Black clays
Black clays
120
120
Swelling pressure SP (kPa)
100
80
60
40
20
n = 7
Cr vs SP
Swelling pressure SP (kPa)
100
80
60
40
20
n = 7
FS vs SP
0
0,80 1,00 1,20 1,40 1,60
Relative consistency Cr
0
80 130 180
Free swell FS (%)
Figure 7.31. Correlation between Cr and SP.
Figure 7.32. Correlation between FS and SP.