Expansive soil is a kind of clay soil that expands rapidly after being immersed in water and shrinks significantly after losing water. The expansive soil slopes exposed to the atmosphere are in the process of continuous dry and wet cycles and are extremely unstable under the conditions of rainfall. Based on saturated-unsaturated seepage theory, the unsaturated seepage process and humidification process of the expansive soil slope under rainfall were simulated, and a related FORTRAN language program was developed. The effects of matrix suction changes, seepage softening, and moistening expansion during the seepage process were considered. The effects of strength attenuation, seepage softening, and moistening expansion on the overall stability of the expansive soil slope were analyzed. The results show that under the action of rainfall, the failure mode of the expansive soil slope after multiple dry-wet cycles is shallow collapse, and the failure surface is located in the weathered area, which is quite different from the traction landslide of the homogeneous expansive soil slope. After considering the moistening expansion and softening effects, the maximum displacement of the slope increased by an order of magnitude, and the safety factor decreased significantly. The significant increase in the horizontal stress of the lower half slope is the main reason for the landslide. The research results well explain the special tractive and shallow properties of typical expansive soil landslides.

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