an engineering geological characterisation of tropical clays - GBV

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Table 7.22. Derived classification of relative degree of swelling of black
clays based on percentage swelling (after author, 2003).
P (kPa) S (%) Swelling degree
0-2,5 100-75 high
2,5-10 75-30,0 moderate
10-50,0 30-10,0 low
> 50,0 < 10 very low
A correlation between percentage swelling and corresponding load decrements (expressed as
percentage of respective swelling pressures) for the individual soil samples is presented
diagrammatically in Fig. (7.35). The variation is generally logarithmic with a very strong
correlation (R = 0,99 – 1,0).
Individual samples: S (%) vs P (%)
120
Loading P (%)
100
80
60
40
R 2 = 0,98
R 2 = 0,99
R 2 = 1,0
SA2-70cm
SB1-70cm
SC25-50cm
SC29-50cm
Logarithmic SA2-70cm
Logarithmic SB1-70cm
20
0
R 2 = 1,0
0 50 100 150
Logarithmic SC25-50cm
Logarithmic SC29-50cm
Swelling S (%)
Figure 7.35. Correlation between percentage swelling and percent loading pressure of
individual black clay samples.
Results of an overall correlation combining results of all samples tested are presented Fig.
(7.36). The relationship between percentage swelling and extent of loading is once again
logarithmic (Fig. 7.36a) with a very strong correlation (R = 0,995), and could be summarised
by an overall equation, i.e.
P = -22,3Ln(S) + 100,8 (7.49)
where P = extent of loading (%)
S = cumulative swelling (%)