Collapsibility Characteristics of a Residual Soil in Matale District, Sri Lanka

Collapse is termed as the large volume reduction taken place in partially saturated soils upon wetting under a particular applied pressure, that are otherwise resistant to much larger applied stresses under normal conditions. This phenomenon can be commonly witnessed in Aeolian, alluvial and colluvial type of soils across the globe though not much reported to occur in residual soils. However, a residual soil too can develop into a collapsible soil under certain conditions. In this study, undisturbed soil samples obtained from a construction site in Matale District, Sri Lanka consisting of a residual soil which exhibited unusually low values of dry density was subjected to a series of double oedometer tests to determine the collapse potential and to investigate the variation of collapse potential with the applied normal pressure, relative compaction and degree of saturation. The study revealed that the collapse potential of different locations of the site is directly proportional to the applied normal pressure and inversely proportional to both relative compaction and degree of saturation. Also, it was identified that samples remolded maintaining their in situ dry density can increase the collapse potential of a slightly collapsible soil. A multi-variate regression analysis was performed to develop a relationship for collapse potential in terms of applied normal pressure, relative compaction and degree of saturation.