Study on Slope Stability of Paleo-Clay Strength Degradation Under Soaking and Wet–Dry Cycles

Due to Paleo-clay’s unique properties and widespread distribution throughout China, it is essential in geotechnical engineering. Rainfall frequently causes the deformation of Paleo-clay slopes, making slope instability prediction crucial for disaster prevention. This study explored Paleo-clay’s strength degradation and slope stability under soaking and wet–dry cycles. Using Mohr–Coulomb failure envelopes from experiments, curve fitting was used to find the patterns of Paleo-clay strength degradation. Finite element simulations and the strength discounting method were used to analyze the stability and deformation of Paleo-clay slopes. The results indicate that wet–dry cycles impact them more than soaking. Paleo-clay’s cohesion decreases exponentially as the number of wet–dry cycles and soaking times rise, but the internal friction angle changes very little. After 10 wet–dry cycles and 24 days of soaking, iron-bearing clay’s cohesion decreased to 17% and 44% and reticular clay’s to 32% and 48%. Based on the study area characteristics, three slope types were constructed. Their stability exhibited exponential decay. Under soaking, stability remained above 1.4; under wet–dry cycles, type I and II stability fell below 1.0, leading to deformation and failure. All types showed traction landslides with sliding zones transitioning from deep to shallow. Practical engineering should focus on the shallow failures of Paleo-clay slopes.