an engineering geological characterisation of tropical clays - GBV

173
%coarse
% coarse fraction variation (< 0,5 m)
1010 6 11 4
1°19´S 4000
Profile distance (m)
9 9 10 16 16 10 10 8
3000
10 11 11 16 6 10 12
2000
West 11 11 7 6 8 10 11
1000
13 12 11 12 6 9 9
26
1°21.5´S 0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
36°49´E
South Profile distance (m)
36°55´E
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
% coarse fraction variation (> 0,5 m)
28 13 12 9 11
1°19´S 4000
Profile distance (m)
10 10 10 16 26
8 9 11
3000
9 9 9 12 8 7 14
2000
West
9 9 8 12 8 8 15
1000
1°21.5´S
10 9 11 14 11 8 9 15
0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
36°49´E
South Profile distance (m)
36°55´E
20
19
18
17
16
15
14
13
12
11
10
9
8
7
%coarse
21
Fig. 8.14. Distribution and variation of coarse fraction in black clays.
The red soils exhibit average clay and fines contents of 21% and 93%, respectively. Despite
the similar proportions of fines in black clays and red soils, the former are found to exhibit
higher plasticity and potential expansiveness relative to the latter. The difference could be
attributed to the predominating type of clay mineral composition, the high content of
smectites (over 90%) rendering the black clays higher swelling capabilities on wetting. The
red soils are mainly kaolinite (over 80%), a clay mineral characterised by limited swelling
capabilities on wetting.
8.7 Shear strength
Variation of strength characteristics in black clays is presented in Figures (8.15a & b) in
which distribution of shear strength parameters of apparent cohesion (c´ ) and angle of
frictional resistance (phi or φ´ ) are given in contour form.