an engineering geological characterisation of tropical clays - GBV

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Plate 7.2a. Apparatus for liquid limit
determination of soil.
Plate7.2b. Liquid limit determination
showing V-shaped groove in soil sample.
The numerical difference beween the liquid limit (LL) and plastic limit (PL) was calculated to
give the plasticity index (PI) of the soil, i.e.
PI = LL – PL (7.5)
Results of liquid limit tests obtained for the soils in this study are reported to the nearest
whole number (1%) alongside those of plastic limit and plasticity index in Table (7.2).
7.1.3.4 Evaluation and application of results
Results of Atterberg limits obtained in this study have been used for physical classification of
the clay soils found (Fig. 7.1), based on the standard plasticity chart or A-line chart (Draft
revision of CP 2001; BS 1377: 1975). The clay soils have been classified into one of five
categories of low plasticity (CL), medium plasticity (CI), high plasticity (CH), very high
plasticity (CV) or extremely high plasticity (CE). Similarly, the silty varieties of soils have
been correspondingly classified and denoted by ML, MI, MH, MV, or ME.
In Fig. (7.1), the black clays involved in this study have been classified as very high to
extremely high plasticity inorganic clays (CV, CE) and silty clays (MV, ME) while the red
soils wholly plot below the A-line and fall in the class of medium to high plasticity silts and
silty clays (MI, MH).