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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The combined influence <strong>of</strong> relative consistency <strong>an</strong>d plasticity indices on the shear <strong>an</strong>gles <strong>an</strong>d<br />
shear strength <strong>of</strong> <strong>clays</strong> is illustrated in Fig. (7.9a). A fair or moderate correlation (R = 0,54)<br />
showing a general increase in shear <strong>an</strong>gles <strong>an</strong>d / or shear strength with <strong>an</strong> increased ratio <strong>of</strong><br />
Cr/PI is observed. There is also <strong>an</strong> improvement in correlation over that based on plasticity<br />
index (Figs. 7.7a & 7.8a) alone.<br />
Black <strong>clays</strong><br />
Angle <strong>of</strong> shear resist<strong>an</strong>ce<br />
φ´ (°)<br />
35<br />
n = 41<br />
30<br />
25<br />
20<br />
R 2 = 0,29<br />
15<br />
10<br />
0,015 0,025 0,035 0,045<br />
Ratio Cr/PI<br />
Shear <strong>an</strong>gle vs Cr/PI<br />
Figure 7.9a. Correlation between <strong>an</strong>gle <strong>of</strong> shear resist<strong>an</strong>ce (φ´ ) <strong>an</strong>d ratio Cr/PI<br />
for black <strong>clays</strong>.<br />
Black <strong>clays</strong><br />
Cohesion c´ (kN/m²)<br />
60,00<br />
50,00<br />
n = 41<br />
40,00<br />
30,00<br />
20,00<br />
10,00<br />
0,00<br />
0,016 0,021 0,026 0,031 0,036<br />
Cr/PI<br />
Cohesion vs Cr/PI<br />
Figure 7.9b. Correlation between cohesion (c´ ) <strong>an</strong>d ratio Cr/PI<br />
for black <strong>clays</strong>.<br />
On the other h<strong>an</strong>d, correlations between values <strong>of</strong> cohesion <strong>an</strong>d those <strong>of</strong> index parameters<br />
(natural moisture content, relative consistency, Atterberg limits) are generally weak, with the<br />
resulting plots giving more spread out data points (Figures 7.6b & c, 7.7b, 7.8b, 7.9b).<br />
All in all, however, the strengths <strong>of</strong> correlations between cohesion <strong>an</strong>d shear <strong>an</strong>gles on one<br />
h<strong>an</strong>d <strong>an</strong>d relative consistency <strong>an</strong>d plasticity indices on the other are generally poor <strong>an</strong>d, at<br />
their best, only moderate. This serves to point to the uncertainities accomp<strong>an</strong>ying assessment<br />
<strong>an</strong>d <strong>characterisation</strong> <strong>of</strong> shear strengths <strong>of</strong> <strong>clays</strong> based on results <strong>of</strong> index tests performed on<br />
disturbed <strong>an</strong>d fractioned / sieved soil samples.