Shear strength properties of a residual soil in Singapore

The shear strength and stress-strain behaviour of residual soil are known to be affected significantly not only by the initial porosity and stress history, but also by the bonds between particles. Although residual soil is commonly encountered during constructions in the tropical region, studies on its engineering properties are far from adequate. There is a lack of in-depth study to characterize the strength and deformation behaviour of intact residual soils in Singapore, especially under more representative testing conditions such as plane-strain conditions. In relation to a tunnelling construction project in Singapore, the engineering properties of an intact residual soil were characterised using laboratory tests. Large block undisturbed soil samples taken from a construction site were used. K ₀ consolidated undrained triaxial compression (CK ₀UC), extension (CK ₀UE), direct simple shear (CK ₀UDSS), and K ₀ consolidated undrained planestrain (CK ₀UPS) tests were conducted. The undrained shear strength ratio c _u/σ ₁₀ and overconsolidation ratio (OCR) relationships were established. The test results indicate that the undrained shear strength (c _u) of the intact residual soil is highly anisotropic in term of c _u/σ ₁₀ ratio. It is also noted from the experimental results that the secant friction angles were highly dependent on consolidation stresses, as well as the testing methods. These anisotropic properties will affect considerably the design methods and the selection of parameters for analyses.