Reactivation mechanism and evolution characteristics of water softening-induced reservoir-reactivated landslides: a case study for the Three Gorges Reservoir Area, China

Geological disasters of reactivated landslides have occurred frequently. Therefore, such landslides’ reactivation mechanism and evolution characteristics of such landslides have become increasingly important. We combined the geological characteristics and failure mode of reactivated landslides in the Three Gorges reservoir (TGR). We found that a permeable sliding surface that can simulate the segmental instability of the sliding zone was developed. The deformation process of reactivated landslides was realized by injecting water into the bottom of the sliding zone. Multi-physical field data were obtained based on volumetric water content sensors, pore pressure converters, and digital image processing. The results showed that (1) The significant decrease in shear strength of the water-saturated sliding zone soil was an essential condition for landslides, and the sudden increase of pore pressure at the sliding surface was a key incentive to activate landslides. (2) Slope deformation was divided into a strong deformation zone, a weak deformation zone, and a retrogressive zone. (3) The landslide instability with the iron-clay sliding zone was mainly controlled by the shear strength of the sliding zone soil. Additionally, the whole sliding was dominant; The landslide instability with the sand-clay sliding zone is unstable under the dual mechanism of strong attenuation of the sliding zone soil and local failure of slope toe. The landslide instability with the clay-sand sliding zone was first damaged at the foot of the slope, then the shear strength attenuation of the sliding zone soil played a significant role in sliding factors. (4) The failure mechanism of reactivated landslides was mainly the combined action of tension-shear failure.