The shear strength and stress-strain behaviour of residual soil are known to be aŠected signiˆcantly 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. K0 consolidated undrained triaxial compression (CK0UC), extension (CK0UE), direct simple shear (CK0UDSS), and K0 consolidated undrained planestrain (CK 0 UPS) tests were conducted. The undrained shear strength ratio c u /s? 10 and overconsolidation ratio (OCR) relationships were established. The test results indicate that the undrained shear strength (cu) of the intact residual soil is highly anisotropic in term of cu/s? 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 aŠect considerably the design methods and the selection of parameters for analyses.

The research work presented in this report was carried out under the supervision of Associate Professor Chu Jian. I would like to express the most sincere gratitude for his inspiration, patience and guidance. His endlessly support and invaluable experience came handy throughout the whole year. His close monitoring and encouragement are especially appreciated. I also extends my heartily appreciation to: The technical staff of Geotechnics labs, especially Mr. Tay Soon Leung, Mr.