Abstract: Under the long-term influence of periodic water level fluctuations in the reservoir, bank collapse and frontal deformation of soil slopes are common geological disasters. By interpreting the hydraulic forcing as the coupled action of repeated wetting-drying cycles and periodic reciprocating seepage, this study employs a self-developed model testing device to construct a gravel slope using discontinuously graded soil. The individual and combined effects of multiple wetting-drying cycles and reciprocating seepage are simulated separately. The loss patterns of fine particles and the evolutionary process of surface cracks on the slope are systematically analyzed. Continuous monitoring of pore water pressure, volumetric water content, and displacement field evolution elucidates the synergistic damage mechanism of cracking and erosion within the hydro-fluctuation zone, as well as their influence on slope deformation and failure. Results indicate that repeated wetting-drying cycles promote the progressive development and pseudo-healing of surface crack networks, whereas reciprocating seepage induces substantial loss of fine particles. Under the alternating combined action of both processes, desiccation cracks compromise soil integrity and create preferential seepage pathways, thereby accelerating fine particle loss. Conversely, seepage erosion exposes coarse skeletal particles, diminishes the capacity for crack healing, and enhances soil permeability. It can be inferred that desiccation crack and erosion interact mutually and exert a synergistic aggravating effect on soil structural degradation, thus promoting the earlier slope failure. This behavior is primarily attributed to the combined driving forces arising from severe soil structure deterioration and seepage pressure. The findings offer a theoretical foundation and technical support for understanding the intrinsic relationship between periodic water level fluctuations and progressive slope deformation, enabling more accurate analysis and prediction of slope stability.

Key words: drying-wetting cycle, seepage erosion, structural damage, shallow failure, physical model test