an engineering geological characterisation of tropical clays - GBV

174
1°19´S 4000
Profile distance (m)
Cohesion (c`) variation (< 0,5 m)
23.1 29.8
47.9 44.0 45.4 32.0
3000
46.7 47.4 44.9 30.2
2000
West 46.4 42.6 25.8 26.0
1000
c` (kN/m²)
46
44
42
40
38
36
34
32
30
1°21.5´S
47.2
11.5 25.1
28
0
26
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
36°49´E
South Profile distance (m) 36°55´E 24
22
20
18
16
1°19´S 4000
Cohesion (c`) variation (> 0,5 m)
35.6 41.0
Profile distance (m)
36.1 35.6 36.1 28.0
3000
28.4
2000
26.3 36.9 28.6
West 40.8 35.1 36.2 29.0
1000
1°21.5´S
31.8 33.7 34.9
0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
36°49´E
South Profile distance (m) 36°55´E
38.5
38
37.5
37
36.5
36
35.5
35
34.5
34
33.5
33
32.5
32
31.5
31
30.5
30
29.5
29
Fig. 8.15a. Distribution and variation of cohesion (c´ ) in black clays.
c` (kN/m²)
There is a slight increase in values of cohesion with increased depths (Fig. 8.15a), and this
could be attributed to a corresponding decrease of organic matter content with depth of soils.
In practice, organic matter would have the effect of counteracting cohesive effects in clay
soils. Similarly, the general decrease in the thickness of black clays eastwards across the study
area would also mean progressively increased counteractive effects of organic matter content
on cohesion of the clays. As a result, values of cohesion are also observed to generally
decrease eastwards at any chosen depth interval (Fig. 8.15a).
The angle of shear resistance is usually a more reliable parameter in characterising strength
characteristics of soils (Head, 1988).