Rainfall-induced landslides in residual soils are common occurrences in Singapore and the region. The two main types of residual soils, which were derived from the Bukit Timah Granite and the Sedimentary Jurong Formation, cover almost two-thirds of Singapore Island. As similar to those in many other parts of the world, they are generally heterogeneous, highly textured in nature, partially saturated and relatively stiff. Although Old Alluvium is considered a kind of residual soil, this paper will concentrate on the residual soils of Bukit Timah Granite and Jurong Formation. A six-grade system, which was proposed by Little (1967, 1969) as a modification to Moye's (1955) original system, is widely accepted and adopted in the British Code of Practice for site investigation (1981). In Singapore the modified weathering grade classifications for both residual soils as adopted by Dames & Moore (1983) during the preliminary study for the Mass Rapid Transit System (MRT) Phase 1 are still largely used in major site investigation works. The laboratory based index properties, particle size distribution, both undrained and drained shear strength properties and permeability characteristics for both types of soils recorded from various locations were analyzed and presented in this paper. The shear strength tests with suction for unsaturated soil are becoming popular in recent years and the available results of sedimentary soil are presented. The engineering properties obtained from available in situ tests were also analyzed and correlated with laboratory based parameters.
The Republic of Singapore consists of a main island and several outlying islands totaling some 620 sq. km in area. The various in situ testings such as Standard penetration tests (SPT), Electrical cone penetration tests (CPT), Swedish weight sounding test (WST), Pressuremeter tests (PMT) and Flat dilatometer tests (DMT) can be used for the determination of engineering parameters including subsurface profilings.
