Evolution mechanism of the ancient Qingshi Landslide from reactivation to self-stabilization under cyclic hydrological loading: insights from coupled hydro-mechanical modeling

Long-term hydrological cycles modify the hydro-mechanical properties of slope soils, ultimately establishing a new equilibrium between deformation and self-adjustment. Given the prevalence of self-adjustment mechanisms in natural bank slopes, a numerical model capturing soil hydro-mechanical responses to hydrological-year variations is essential. The study developed a coupled mechanical-hydraulic model capable of simulating multi-year hydrogeological effects, informed by laboratory-derived hydraulic characteristics and shear strength parameters, to investigate the self-stabilization mechanism of the reactivated Qingshi landslide. Although local engineering measures were implemented at the landslide's front in 2011 and 2014, they did not properly address the main slip zone. Our results indicate that: (i) The primary external drivers of landslide deformation are seasonal rainfall and reservoir water level fluctuations, which jointly alter the internal seepage and stress fields within the landslide body. (ii) Despite the lack of intervention at the main slip zone, the slip zone soils exhibited significant self-stabilizing behavior under long-term wetting-drying cycles. The displacement fields and stability evolution derived from numerical simulations closely align with field monitoring data. This agreement confirms the landslide's self-stabilization behavior to be the key mechanism for achieving a new equilibrium, given the unaltered slip zone.