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