Seepage and deformation characteristics of sliding-zone soils under cyclic seepage pressure

Numerous incidents and failures of landslides in reservoir areas are attributed to water level fluctuations, which frequently induce cyclic changes in seepage pressure within the soil masses. Under such complex cyclic seepage conditions, the hydro-mechanical behavior of sliding-zone soils may significantly differ from that observed under steady seepage conditions. However, the seepage characteristics and deformation behavior of sliding-zone soils experiencing cyclic seepage pressure are not yet fully understood. In this study, we conduct cyclic seepage pressure tests under isotropic consolidation to investigate the variation in hydraulic conductivity and volumetric strain of sliding-zone soils. The results show that the hydraulic conductivity of the sliding-zone soil samples fluctuates under cyclic seepage pressure, with the magnitude increasing as seepage pressure amplitude rises and decreasing with higher confining pressure. Additionally, the volumetric strain of the sliding-zone soil samples exhibited notable fluctuations under cyclic seepage pressure, with the magnitude of the fluctuations intensifying as the seepage pressure amplitude increased. The cumulative volumetric strain and irrecoverable volumetric strain of the samples are higher compared to those observed under steady seepage pressure. Subsequently, hysteresis loops are classified into three types, each indicating distinct deformation characteristics. Finally, the micromechanism of sliding-zone soil under cyclic seepage pressure, considering the effect of physicochemical reactions on pore structure, is revealed to interpret better the intrinsic mechanism of seepage characteristics and deformation behavior. These findings provide a theoretical basis for further accurately evaluating reservoir landslide stability under fluctuating water levels.