Investigating the mechanical behaviour of two residual soils from Malaysia

Yow Loong Kok, Cambridge University
Geotechnical Engineering Group


A laboratory study was performed to investigate the mechanical behaviour of two residual soils from Malaysia. Hand-cut block samples were collected of metasedimentary and granitic residual soils that have formed from the weathering of phyllite and granite parent rocks respectively. Partial saturation is an important aspect of their characteristics in situ. In this research the degree of saturation was artificially elevated, taking precautions against disturbing the structure of the soils, so that any air present existed in occluded bubble form. With air in this form traditional soil mechanics for fully saturated soils can be applied. The main aim of the research described in this thesis is to investigate the mechanical characteristics of the residual soils without additional complexities caused by partial saturation

Scanning electron microscopy examination showed that as an effect of weathering, the soil particles were reduced in size and porosity was increased. The basic characteristics between the two residual soils were quite different because of their different formation modes

High quality intact samples were used in the oedometer and triaxial testing. Reconstituted samples (destructured) were tested to investigate the effects of structure in the intact soils. The results show that the intact samples exhibited a yield stress that was not seen in the reconstituted samples, in which their yielding behaviour could be described with the framework of small-strain kinematic sub-yield surfaces. Greater stiffnesses were observed in the intact soils at pre-yield levels. It was found that the intact soils exhibited a peak friction angle greater than the critical state friction angle. The effects of structure allowed the intact state boundary surface to envelope the intrinsic state boundary surface. Shear band failure was noted in the intact metasedimentary samples, whilst bulging and necking failures were noted in the intact granitic samples. Void ratio which was increased by weathering, has a direct influence on the in-situ mean effective stress and yield stress, and controls the position of the compression curve in the metastable or stable space