an engineering geological characterisation of tropical clays - GBV

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PI = 1,88*LS
A comparison of plasticity index values calculated using the above relationship (PILS) with
those actually measured in the laboratory (PImeasured) has shown and confirmed a strong
agreement in the two sets of data in the form of
PImeasured = 1,005PILS
The plasticity index of red soils could also be estimated from laboratory measured linear
shrinkage using a new relationship developed for the soils, i.e.
PI = 1,84LS
The so calculated and/ or estimated plasticity indices have also been found to be practically
identical to actual laboratory measured values, i.e.
PImeasured = 1,00PILS
Another new relationship has been developed for the estimation of plasticity index (PI) of
black and red soils from laboratory measured values of liquid limit (LL) with a high degree of
approximation, i.e.
PI = 0,79(LL-25)
The so calculated and laboratory measured plasticity indices have been found to be in near
perfect agreement, i.e.
PImeasured = 0,99PILL
Linear shrinkage values could also be estimated by calculation from laboratory determined
liquid limits of black clays and red soils using the newly developed relationship below, i.e.
LS = 0,39(LL-21)
The calculated and laboratory measured linear shrinkage values have been found to be in very
strong agreement, i.e.
LSmeasured = 0,997LSLL
The swelling capability of black clays and red soils, in terms of free swell (FS), could be
estimated with a high degree of approximation by calculation from laboratory determined
Atterberg limits (LL, PI) and linear shrinkage (LS). The new derived relationships take the
form of
FS = 3,17(LL-45),
FS = 3,79(PI-13) and
FS = 7,29(LS-7)