Study on water softening characteristics and multi-stage sliding zone reactivation mechanism of old clay landslides in the Three Gorges Reservoir area subjected to groundwater

The reactivation events of old landslides in the Three Gorges Reservoir area occur frequently, making it imperative to study the water softening characteristics and reactivation mechanism. An old clay landslide was selected as the focus of the research, and a segmented water injection permeable sliding surface was designed to simulate the formation and evolution of the old sliding zone during the process of groundwater rise. Volumetric water content sensors, pore water pressure gauges, high-speed camera devices, and Geopiv-RG digital image processing technology were used to obtain data on multiple physical fields. The analysis results indicated that the decrease in shear strength of the sliding zone soil and the sudden increase in pore water pressure on the sliding surface were important factors in the reactivation of old landslides. The surface deformation exhibited prominent zoning characteristics, primarily categorized into zones of strong deformation, weak deformation, and traction deformation. The failure mechanism involved shear sliding at the front edge, tensile cracking and failure at the trailing edge, and shear creep in the middle section. The development of multi-stage secondary sliding zones in old landslides can be categorized into three types: parallel to the original old sliding zone, partially overlapping with the original sliding zone to form a layered landslide, and completely overlapping with the original sliding zone, indicating overall reactivated deformation.