Model test study on the deformation and stability of rainfall-induced expansive soil slope with weak interlayer

Rainfall infiltration softens the filling material of deep cracks in expansive soil, significantly reducing its mechanical strength and causing slope instability and failure. Investigating this influence is crucial for preventing slope disasters. This study established a model with a weak interlayer to conduct rainfall infiltration tests on an expansive soil slope. Analyzing the moisture absorption and deformation model test results, the study delved into the temporal and spatial variations of the slope’s seepage field. It also clarified the evolution characteristics and action modes of the strain field under seepage influence. Results indicate that runoff leads to pooling at the slope foot, causing significant softening and swelling. The seepage and deformation fields exhibit a “start-rapid growth-slow growth-tend to stability” pattern on the time curve. Soil affected by rainfall infiltration is concentrated at depths of 10–20 cm. The start-up stage of deep soil displacement change is primarily due to water infiltration delay, intensifying with depth. The weak interlayer weakens and is destroyed after moisture absorption, resulting in the upper slope losing support force, leading to continued collapse and slope failure. The research provides a systematic understanding of the mechanism and failure mode of slope disasters, verifying and analyzing permeability, swelling, shrinking, and seepage characteristics of expansive soil.