Abstract: The stability of deeply excavated canal slopes in expansive soil is governed by groundwater-level fluctuations, wetting–drying cycles, and inherent fissures. To investigate these effects, a hydraulic response model test was conducted on a slope with inherent fissures. The left side of the slope contained fissures, whereas the right side remained intact for comparison. The experiment included four wetting–drying cycles, groundwater-level variations, and one prolonged rainfall event. The results showed that: 1) fissures altered the water distribution, resulting in pronounced spatial variations in water content on the left side, whereas the right side became more uniform after prolonged rainfall; 2) the pore water pressure in the deep soil was primarily controlled by the groundwater level, and the response was stronger on the left side; 3) the matric suction of the deep soil on the left side exhibited a response pattern different from that induced by wetting–drying cycles alone; 4) matric suction continuously decreased with increasing wetting–drying cycles, reducing shear strength and accelerating slope displacement, with a lag in the displacement response. The combined effects of groundwater-level fluctuations and inherent fissures intensified the deformation and failure of the slope.

Key words: slope, expansive soil, matric suction, pore water pressure, fissures, wetting-drying cycle, groundwater