an engineering geological characterisation of tropical clays - GBV

187
Red clays; measured/ calculated plasticity index
23
22
n = 8
Measured plasticitx index (%)
21
20
19
18
17
16
PImeas. = 1,00PILS
PImeas. = 0,86PIBS
PI(BS) vs PI meas.
PI (LS) vs PI meas.
15
15 17 19 21 23 25
Calculated plasticity index (%)
Figure 10.4. A correlation of calculated and laboratory measured
plasticity indices of red soils.
10.2 Liquid limit and plasticity index
The plasticity index of black clays and red soils involved in this study could be estimated by
calculation from laboratory determined results of liquid limit using the British Standard
relationship
PI =0,73(LL-20) (10.14)
through which they are very strongly interrelated, i.e.R = 1 (Fig. 10.5). A correlation of
laboratory determined values of plasticity index and liquid limit have also given rise to a new
and strong (R = 0,96) relationship, i.e.
PI = 0,79(LL-25) (10.15)
Diagram: plasticity index/ liquid limit
Plasticity index PI (%)
60
50
40
30
20
10
0
n = 90
PIBS = 0,73(LL - 20)
R 2 = 1
PI = 0,79(LL - 25)
R 2 = 0,92
40 60 80 100
Liquid limit LL (%)
PI British Std
Black+red soils
Fig. 10.5. Correlation: laboratory measured values of plasticity index
and liquid limit of black clays and red soils.