Behaviour of unsaturated soils under direct shear and triaxial compression

The objective of the research reported herein is to investigate the behavior of slider block-basal and slider block-interslice springs proposed in Wong's landslide model. Studies of the characteristics of the two springs quantify equations for describing their stiffness and strength behaviors to be proposed. The test results show a significant drop in the stiffness and strength of the three soils studied with decreasing matric suction at low net confining stress ranging from 0 to 100 kPa. This response is confirmed by applying the proposed shear strength equation to a slope stability analysis in Sunnyside Hill, Calgary. The decrease of the factor of safety to 1.0 or below at this site associated with the decrease in the soil strength caused by a decrease of matric suction to 5 kPa or below recorded in the field measurements. The back analysis exercise suggests that the previous landslides in 1997 and 1998 might happen due to loss in matric suction.