an engineering geological characterisation of tropical clays - GBV

167
Free swell variation; 0,50m depth and greater
Free swell (%)
160
140
120
100
80
60
40
20
0
0 2000 4000 6000 8000 10000 12000
Distance along profile (m)
Profile A
Profile B
Profile C
Profile D
Profile E
Figure 8.9b. Free swell variation across the study area at depths of 0,50m
and greater (north-south distance: 4000 m).
The two sets of data obtained for depths of less than 0,50m and those of 0,50m and over, are
generally comparable and similar in their distribution in terms of maximum and minimum
values as well as their range. A slight variation is, however, exhibited in terms of the median,
mode and mean values as well as the standard deviation and variance. As a result, a
covariance of 35,52 and relatively weak correlation of 0,39 has also been recorded for the two
sets of data. Relatively lower values of free swell and/ or swelling capability in upper soil
depths could be attributed to increased organic matter content.
Fig. (8.10) shows a contoured representation of the above described distribution, in which
patches of low swelling capabilities are associated with lateritic clays; as well as clays of
swampy environments and/ or those adjacent to river valleys and stream channels with
impeded drainage and relatively higher organic matter content.
Free swell values obtained for red soils in this study are comparatively low and range from
15-20%.