Unsaturated shear strength behaviour under unconsolidated undrained tests

Abstract

Residual soils cover more than three-quarts of the land area of Peninsular Malaysia. Many steep slopes in these residual soils often have a deep ground water table. Above those ground water tables, the soils are in unsaturated conditions. In this study, unsaturated shear strength behavior of a tropical residual soil under different stress levels is investigated by using uncomplicated testing procedure. Existing triaxial tests use translation technique for determining unsaturated shear strength parameters but ordinary Unconsolidated Undrained triaxial tests were carried out due to lacking of the advanced testing unit in the laboratory. The Unconsolidated Undrained tests were carried out under different cell pressures at different suctions values to obtain the undrained compressive strengths of the specimens. Preliminary results of the consolidated isotropic undrained tests, show effective cohesion and effective angle of friction i.e., saturated shear strength parameters were 9 kPa and 23°, respectively. In Unconsolidated Undrained tests, the values of apparent shear strength at high stress levels range from 66.1 - 72.6 kPa. At low stress levels, the range of apparent shear strength values was obtained in between 53.1 - 57.5 kPa. The value of friction angle for the highest suction pressure tested in this study (300 kPa) was determined 9.9°. This study illustrated that there is nonlinear relationship between the apparent shear strength and suction.