ESTIMATION OF SHEAR STRENGTH OF GRAVELLY AND SANDY SOILS FROM SHALLOW LANDSLIDES

This study seeks to investigate the unsaturated shear strength of six gravelly and sandy soils collected from shallow landslides in New South Wales, Australia. Results from a series of shear box tests on unsaturated soil specimens revealed that changes in water content (from 0% to 30%) could significantly reduce the shear strength of soil (by 34% to 43%). The observed increases in soil's apparent cohesion and friction angle were attributed to more pronounced effects of suction at low values of water content. The obtained laboratory data were compared with the shear strength estimates obtained by two published models for estimating shear strength. One of the methods was refined to provide a more simplified approach to obtain the air entry value (AEV) using the soil basic parameters. In addition, a new simplified method was proposed to predict the shear strength of unsaturated gravelly and sandy soils using the soil gradation characteristics. Comparisons made between the laboratory data and numerical methods showed a good agreement between the predicted and experimental values across a large range of matric suction which was within 35%.