Drained Residual Strength for Landslides

Drained residual shear strength is considered applicable for the analysis of slopes with a preexisting shear surface. Torsional ring and direct shear tests were performed to investigate the gain in strength, if any, along a preexisting shear surface with time. This study shows that after establishing the drained residual strength conditions, a measureable strength greater than the drained residual strength is obtained in both torsional ring and direct shear tests at effective normal stresses of 100 kPa or less. However, the recovered strength observed in the laboratory is lost after a small shear displacement which suggests that any strength gain may not be relied upon for stabilization purposes so the drained residual strength as measured using ASTM D6467 is recommended for landslide analysis and design.