Experimental study on the macroscopic and microscopic properties of the sliding zone soil in the Huaipa landslide under wetting-drying cycles

Landslides in the Yellow River basin are frequently triggered by periodic rainfall and groundwater fluctuations, processes that progressively degrade the mechanical properties of sliding zone soil. This study investigates the multi-scale deterioration mechanism of sliding zone soil from the Huaipa landslide in Henan Province through integrated wetting-drying cycle tests, direct shear tests, and scanning electron microscopy. The results indicate that the first wetting-drying cycle induces the most significant reduction in shear strength and cohesion. The deterioration rate subsequently decelerates with increasing cycles, tending toward stabilization after seven cycles. Microscopic analysis reveals that wetting-drying cycles initiate and propagate internal fissures, transforming micropores into larger pores and disrupting inter-particle cementation. This study elucidates the correlation between macroscopic strength decay and microscopic structural evolution, thereby providing a theoretical basis for the stability evaluation and disaster mitigation of landslides in reservoir areas.