Effects of overconsolidation on the reactivated residual strength of remoulded deep-seated sliding zone soil in the Three Gorges Reservoir Region, China

Due to the landslide-prone geological conditions, many landslides have occurred in the Three Gorges Reservoir Region (TGRR), most of which are slow-moving ancient landslides characterized by preexisting shear surfaces. In this study, with the purpose of making full use of reactivated residual strength to prevent and treat the slow-moving landslides, such as designing anti-slide piles, the Huangtupo landslide as a typical reactivated ancient landslide in the TGRR was selected to study the overconsolidation (OCR) effect on the reactivated residual strength of deep-seated sliding zone soil by conducting a series of laboratory ring shear tests. It was found that after a short rest of one day, the reactivated residual strength increased with the increase of OCR under a given normal effective stress, but it was lost after a small shear displacement. The overconsolidation effect on reactivated residual strength at a lower stress was more prominent than that at a higher stress. Very coarse sand with a size of 1–2 mm inside the remoulded deep-seated sliding zone soil sample exerts direct control on the reactivated residual strength, and it significantly influences the overconsolidation effect on reactivated residual strength. The results could provide a reliable scientific basis for improving the stability analysis and reinforcement measures of the slow-moving landslides in the TGRR, as well as can be applied to similar slow-moving landslides in other areas.