Residual soils are weathering products of rocks that are commonly found under unsaturated conditions. The properties of
residual soils are a function of the degree of weathering. A series of index properties, engineering properties, mercury
porosimetry tests and scanning electron microscope (SEM) examinations were performed on residual soils from two major
geological formations in Singapore. The results indicate that the variation in the index and engineering properties as well as
microstructural characteristics of the residual soils with depth can be related to the degree of weathering. An increase in the
degree of weathering results in an increase in pore volume and produces a larger range of pore-size distribution. The variation in
the pore volume and the pore-size distribution through a profile of weathered rock can be used as an indicative measure of the
variation in the degree of weathering with depth.