an engineering geological characterisation of tropical clays - GBV

154
swelling pressures exhibited by these clays when allowed access to water are therefore a
result of the high content of expansive clay minerals (smectites) found within, rather than
overconsolidation character.
The black clays studied and sampled during the dry season were observed to exhibit strong
dessication cracks and a firm to stiff, sometimes hard consistency in the field. Later laboratory
studies have shown the clays to posses high swell and expansion potential by exhibiting large
percentage swelling and high swelling pressures when allowed free access to water (Table
7.19; Fig. 7.28). The appreciable amount of swelling and swelling pressures which develop on
saturation of the soils with water could be due partly to some form of slight seasonal
overconsolidation of black clays, previously preconsolidated by effects of lowering of the
ground water table and partial drying during the hot and dry season; and partly to the high
smectite content, as already stated.