an engineering geological characterisation of tropical clays - GBV

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Black clays: P (kPa) vs S (%)
Pressure load P (kPa)
90,00
80,00
70,00
60,00
50,00
40,00
30,00
20,00
10,00
0,00
0 20 40 60 80 100 120
Swelling S (%)
SA2/70cm
SB1/70cm
SC25/50cm
SC29/50cm
Figure 7.34. Variation of percentage swelling of black clays with loading pressures.
A classification of the relative degree of swelling achieved under various loading pressure
decrements for each of the soil samples tested is given in Table (7.21). As a result, a general
classification for the black clays as a whole, has been derived and presented in Table (7.22). It
is observed that black clays would exhibit high percentage swelling when externally loaded to
below 5 kPa; and very low percentage swelling when loaded to over 80 kPa. This implies that
external engineering structures imposing loads of up to 5 kPa and less would still give way to
maximum swelling of the clays on wetting, with a corresponding maximum destabilisation of
the same structures. However, the structures would be relatively more stable when designed to
impose loads of over 80 kPa.
Table 7.21. Relative degree of swelling of black clays under various load
decrements.
Swelling degree
Sample No. S (%) P (kPa) (after author, 2003)
SA2/70cm 100-52 0-4,96 high
52-31 4,96-10 moderate
31-0 10,0-82,46 low
SB1/70cm 100-85 0-1,18
high
85-30 1,18-10 moderate
30-0 10,0-37,48 low
SC25/50cm 100-75 0-1,70 high
75-34 1,70-8,75
moderate
34-0 8,75-36,23 low
SC29/50cm 100-85 0-1,58 high
85-30 1,58-11,24 moderate
30-0 11,24-44,98 low