an engineering geological characterisation of tropical clays - GBV

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The results of correlation show that liquid limit, LL, would be a better estimator of the
compression index and compressibility of soils than the plasticity index, PI, (Table 7.15b).
The strength of correlation between cc and LL is very high (R = -0,85) for the black clays; but
is reduced to moderate (R = -0,58) for combined black clays and red soils (Figs. 7.23 and
7.24). The relationships between compression index and liquid limit take the form of
cc = 0,0099(122-LL) (7.47)
for black clays, and
cc = 0,0016(308-LL) (7.48)
for both black clays and red soils.
Table 7.15b. Results of compression indices correlated with Atterberg limits.
Sample No. Load
(kPa) Wn (%) LL (%) PI (%) Cc Approx. Compressibility
SA2-70cm 100-2400 34 90 54 0,3 medium-high
SA37-50cm 25-1600 22 83 44 0,4 medium-high
SB1-70cm 50-2400 30 90 51 0,29 medium-high
SB42-50cm 100-2400 21 91 47 0,34 medium-high
SC17-50cm 100-2400 22 81 48 0,44 medium-high
SC29-50cm 100-2400 20 80 43 0,38 medium-high
RD1-30cm 12,0-2400 39 49 18 0,42 medium-high
RD1-100cm 12,0-2400 24 51 21 0,4 medium-high
RD1-400cm 12,0-2400 25 48 18 0,39 medium-high
Correlations (R) Black & red soils -0,58 -0,55
Correlations (R ) Black clays only -0,85 -0,66
Results of correlations and analysis show that cc values generally decrease with increasing
liquid limit and plasticity index of soils ( Table 7.15b; Figs. 7.23 & 7.24). This serves to
suggest that compressibility of soils generally decreases with increased plasticity, and vice
versa.