Reactivation mechanism of ancient giant landslides in the tectonically active zone: a case study in Southwest China

The reactivation mechanism and stability of ancient landslides are the major concerns in the tectonically active zone. A detailed case study has been conducted to examine the reactivation mechanism of ancient landslides in Southwest China by investigating the reactivation process, shear strength and stability. Field investigation suggests that the reactivation of ancient giant slides, such as the Luosiwan slide, is attributed to the cumulative effect of adverse geological, structural condition and intensive artificial processes. However, long-term observation has shown that the ancient giant landslides usually remain stable in the remote area in spite of such adverse conditions. Ring shear tests also indicate high peak shear strength of the sliding zone soils. However, the shear strength decreases significantly once displacement occurs at the toe of giant landslide due to engineering construction. The construction process could be considered as the critical triggering factor for the reactivation of ancient giant landslide, which exerts sudden changes in the forces acting on the slope. Both long-term adverse geological evolution and sudden change in the strength lead to the reactivation of giant landslide. This study also suggests that liquefaction plays an important role in the failure behavior of reactivated ancient landslide. An effective drainage system has to be set up during engineering construction so as to reduce the probability of reactivation of ancient landslides.