an engineering geological characterisation of tropical clays - GBV

160
Liquid limit (LL) variation (< 0,5 m)
36°55´E
LL (%)
1°19´S
Profile distance (m)
West
1°21.5´S
36°49´E
LL%
88
87.5
87
86.5
86
85.5
85
84.5
84
83.5
83
82.5
82
81.5
81
80.5
80
79.5
79
78.5
South
Profile distance (m)
Fig. 8.4a. Block diagram showing distribution and variation of liquid limit values at depths of
less than 0,5m in black clays.
A contoured representation of the distribution is shown in Figures (8.4a & b) in which
isolated patches of relatively low liquid limits correspond to zones of more lateritic clays
and/or swampy environments. On the whole, however, there is a slight tendency of liquid
limit values to increase with depth. This could be attributed to the relatively higher organic
matter content of black clays for depths of less than 0,50m, and which has the effect of
inhibiting the plasticity of soils. As a result, soil depths of less than 0,50m show median,
mode and mean liquid limit values of 84%, 85%, and 84%, respectively, as well as standard
deviation of 3,30 and variance of 10,90; while soil depths of 0,50m and greater, exhibit
relatively larger median, mode and mean values of 87%, 89% and 86%, respectively. The
latter soil depths are also characterised by standard deviation of 4,11 and variance of 16,86.
On the whole, however, the two sets of data at the two different depth intervals are generally
comparable and in good agreement, this being indicated by a covariance of 8,28 and a fairly
strong correlation of 0,63 (Table 8.1).