Effect of Local Cyclic Loading on Direct Shear Strength Characteristics of Shear-Zone Soil

The reservoir landslide in the Three Gorges Reservoir Area (TGRA) often suffers from local cyclic loading scenarios produced by surge waves, groundwater level fluctuation, traffic loading, and seismic activity. However, the effects of local cyclic loading on the shear resistance of the shear-zone of the reservoir landslide are poorly understood. This study experimentally investigates the effects of local cyclic loading on the shear strength and the deformation of shear-zone material using cyclic direct shear tests. A series of cyclic direct shear tests are performed with different normal stresses, cyclic periods, and numbers of cycles. The experimental results indicate that: (1) Compared with monotonic loading, local cyclic loading can significantly decrease the shear stress of shear-zone soil. (2) Shear-zone soil exhibits greater volumetric contraction under local cyclic loading conditions than that under monotonic loading. (3) Under different vertical stresses, the differentiation of shear deformation after 40 cycles of loading was slight and virtually insignificant. The research results reveal the weakening law of the mechanical strength of shear-zone soil under local cyclic loading, which provides a foundation for investigating the mechanism of the reservoir landslide under the fluctuation of water levels.