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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Table 7.17. Classification <strong>of</strong> black <strong>clays</strong> <strong>an</strong>d red soils based on coefficient <strong>of</strong> secondary<br />
compression.<br />
Coeff. <strong>of</strong><br />
secondary<br />
compression Average<br />
Category Sample No. cα value cα Clay type<br />
Typical examples < 0,001 Overconsolidated <strong>clays</strong><br />
<strong>of</strong> <strong>clays</strong> 0,005-0,02 Normally consolidated <strong>clays</strong><br />
(after Lambe & 0,03 <strong>an</strong>d over Very plastic <strong>clays</strong> <strong>an</strong>d/ or<br />
Whitm<strong>an</strong> –1979)<br />
org<strong>an</strong>ic <strong>clays</strong><br />
SA2-70cm 0,0002-0,011 0,006 Normally consolidated <strong>clays</strong><br />
This study: SA37-50cm 0,003-0,017 0,009 Normally consolidated <strong>clays</strong><br />
Black <strong>clays</strong> SB1-70cm 0,0002-0,012 0,005 Normally consolidated <strong>clays</strong><br />
SB42-50cm 0,005-0,024 0,014 Normally consolidated <strong>clays</strong><br />
SC17-50cm 0,006-0,02 0,012 Normally consolidated <strong>clays</strong><br />
SC29-50cm 0,003-0,014 0,008 Normally consolidated <strong>clays</strong><br />
RD1-30cm 0,002-0,004 0,003 Slightly overconsolidated <strong>clays</strong><br />
This study: RD1-100cm 0,003-0,008 0,006 Normally consolidated <strong>clays</strong><br />
Red soils RD1-400cm 0,002-0,007 0,004 Slightly overconsolidated <strong>clays</strong><br />
Results <strong>of</strong> swell index, Cs, obtained for black <strong>clays</strong> <strong>an</strong>d red soils during unloading phase <strong>of</strong><br />
oedometer tests are summarised in Table (7.18). The black <strong>clays</strong> generally exhibit higher<br />
swelling capabilities <strong>an</strong>d/ or exp<strong>an</strong>sion tendencies (Cs = 0,03-0,075; me<strong>an</strong> value = 0,054) on<br />
unloading th<strong>an</strong> the red soils (Cs = 0,02-0,03; me<strong>an</strong> value = 0,027). Correlations between swell<br />
indices <strong>an</strong>d index properties (liquid limit, plasticity index, free swell) are generally poor<br />
(Figures 7.25, 7.26 & 7.27). This implies that uncertainties would be encountered in trying to<br />
assess <strong>an</strong>d/ or predict soils swelling <strong>an</strong>d/ or exp<strong>an</strong>sion tendencies based on results <strong>of</strong> index<br />
tests performed on disturbed <strong>an</strong>d fractioned samples.<br />
Table 7.18. Results <strong>of</strong> swell indices for black <strong>clays</strong> <strong>an</strong>d red soils correlated with Atterberg<br />
limits <strong>an</strong>d free swell.<br />
Sample No. Load kPa Wn (%) LL (%) PI (%) FS (%) Cs<br />
SA2-70cm 100-2400 34 90 54 170 0,07<br />
SA37-50cm 25-1600 22 83 44 115 0,075<br />
SB1-70cm 50-2400 30 90 51 145 0,043<br />
SB42-50cm 100-2400 21 91 47 145 0,03<br />
SC17-50cm 100-2400 22 81 48 110 0,04<br />
SC29-50cm 100-2400 20 80 43 110 0,065<br />
RD1-30cm 12,0-2400 39 49 18 20 0,03<br />
RD1-100cm 12,0-2400 24 51 21 15 0,03<br />
RD1-400cm 12,0-2400 25 48 18 15 0,02<br />
Correlations (R ) Black & red soils 0,61 0,64 0,63<br />
Correlations (R ) Black <strong>clays</strong> only -0,34 -0,14 -0,06<br />
Diagramatically, the generally weak correlations are reflected in terms <strong>of</strong> plot points which<br />
tend to be more spread out (Figures 7.25, 7.26 & 7.27).
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