Pore-scale structure evolution and creep behavior of sliding-zone soil under cyclic seepage pressure

Many reservoir landslides tend to remain in a creep state under periodic water level fluctuations, with the sliding zone acting as the weakest structural layer controlling overall deformation. Understanding the creep behavior of sliding-zone soils under cyclic seepage pressure (CSP) and the associated mechanisms is therefore essential for assessing the long-term deformation and stability of reservoir landslides. In this study, seepage and triaxial creep tests were conducted to investigate the pore structure evolution and creep behavior of sliding-zone soils subjected to CSP. Computed tomography (CT) was employed to quantitatively characterize the pore structure, including porosity, pore size distribution, pore shape, and pore throat distribution. Results reveal that CSP promotes a more uniform spatial distribution of pores with predominantly flaky morphology, facilitating the formation of a connected pore network in which small-area pore throats serve as primary seepage pathways. Under CSP, the soil exhibits a distinct ‘‘stick-slip’’ creep behavior that accelerates the creep rate while reducing the total creep deformation. When the deviatoric stress is lower than the CSP amplitude, the creep response fluctuates markedly, whereas at stresses exceeding 900 kPa, the effect of CSP becomes negligible. These findings offer a new perspective on the creep mechanisms of reservoir landslides influenced by water level variations and establish a theoretical basis for precise evaluation of their long-term stability.