an engineering geological characterisation of tropical clays - GBV

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Cumulative log-time/settlement
curves: black clays (SA2-70cm)
Cumulative log-time/settlement
curves: Red soils (RD1-100cm)
cumulative settlement (mm)
time - minutes (log scale)
0,1 10,0 1000,0 100000,0
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
2,2
cumulative settlement (mm)
0,100 10,000 1000,000
0,000
1,000
2,000
3,000
4,000
5,000
time - minutes (log scale)
100000,0
00
2,4
2,6
6,000
2,8
3
Fig. 7.16. Conventional log-time/settlement
curves for black clays during loading
and unloading stages.
7,000
Fig. 7.17.Unconventional log-time/settlement
curves for red soils during loading
and unloading stages.
Results of voids ratio change of soils during loading and unloading stages are summarised in
the form of voids ratio/ log pressure (e/log p) curves as shown in Figure (7.18). The curves
for the red soils are generally placed higher up the diagram, implying higher voids ratios and
porosities. On the other hand, e/log p curves for black clays occupy lower positions on the
diagram due to their relatively lower voids ratios and porosities. As a result, red soils would
be expected to be more compressible than the black clays over the same loading range. In
addition, unloading portions of the curves are more or less flat and/ or horizontal for the red
soils, while those for black clays are relatively steeper. This serves to show once again the
higher potential swelling capabilities of black clays relative to those of red soils.