Back-Analysis of Preexisting Landslides

Drained residual shear strength is applicable to slopes containing preexisting shear surfaces and preexisting landslides. Laboratory ring shear testing by various researchers suggest the possibility of strength gain along preexisting shear surfaces which had previously obtained a residual strength condition. This paper presents back-analysis of two case histories that were used to suggest strength recovery to confirm test results developed herein and explain how the recovered strength may be useful in understanding slope behavior during the rest period and movement reactivation. These back-analyses are important to determine whether or not strength gain occurs and the practical significance, if any, of the strength gain in design of the remedial measures.