an engineering geological characterisation of tropical clays - GBV

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Table 7.14. Rates of consolidation-settlement of black clays and red soils.
Category
Clay type/ Sample No.
Coeff. of consolidation cv
(m²/year)
Rate of consolidationsettlement
Typical examples High plasticity 0,1-1,0 low
for inorganic clays Medium plasticity 1,0- 10 Medium
(after Lambe & Low plasticity 10-100 High
Whitman –1979) Silts > 100 very high
SA2-70cm 0,07-5,08 low - medium
This study: SA37-50cm 0,05-1,73 low -medium
Black clays SB1-70cm 0,19-2,36 low -medium
SB42-50cm 0,06-0,494 low
SC17-50cm 0,07-0,56 low
SC29-50cm 0,104-1,97 low -medium
RD1-30cm 1,38-11,85 medium to high
This study: RD1-100cm 1,18-4,67 medium
Red soils RD1-400cm 2,71-12,14 medium to high
Variations of values of mv, cv and K with increased loading during oedometer consolidation
tests have also been investigated by plotting them mid-way between applied pressure (log
scale) values (Figs. 7.19, 7.20, 7.21 and 7.22), since they relate to increase from one loading
stage to the next.
7,000E-09
K/ log p curves: black clays & red soils
6,000E-09
Permeability K (m/s)
5,000E-09
4,000E-09
3,000E-09
2,000E-09
1,000E-09
0,000E+00
1 10 100 1000 10000
Log pressure (kPa)
SA2-70cm (black clays) SA37-50cm (black clays) SB1-70cm (black clays)
SB42-50cm (black clays) SC17-50cm (black clays) SC29-50cm (black clays)
RD1-400cm (red soils)
Figure 7.19. Permeability/ log pressure (K/log p) curves for black clays and red soils.
In Fig. (7.19), the K/ log p curves of the red soils generally plot higher up the diagram than
those of black clays, and this especially at the initial stages of loading. This serves to indicate
the generally higher permeability of red soils relative to the black clays. However, the
permeability of red soils is also observed to decrease with increased depth (Fig. 7.20), and this