Probabilistic Stability Analysis of Retaining Walls with Unsaturated Backfill

The stability of retaining walls is strongly affected by the mechanical and hydraulic behavior of unsaturated backfill soils, where the interactions between suction, moisture content, and external loading introduce significant uncertainties. Conventional deterministic limit equilibrium analyses fail to capture these uncertainties and neglect correlations between different failure modes. This study presents a probabilistic framework to assess the stability of rigid retaining walls backfilled with unsaturated soil under steady-state flow and uniform surcharge loading. Utilizing Monte Carlo simulations, the framework incorporates the variability in soil–water retention curve parameters, shear strength, and hydraulic conductivity of both backfill and foundation soils into the limit equilibrium analysis of the wall. The proposed method evaluates the probabilities of individual failure modes (sliding, overturning, and bearing capacity) and system-wide failure and examines cross correlations between factors of safety. Additionally, the analysis integrates the effect of tension cracks as a random variable. The framework is applied to a typical cantilever retaining wall, and sensitivity analyses are conducted to evaluate the impact of various parameters. The results demonstrate the critical influence of uncertainty in soil properties on retaining wall stability. Suction effects were found to increase the correlation between the depth of tension cracking and all factors of safety while reducing the correlations between factors of safety for overturning versus sliding and overturning versus bearing capacity. This probabilistic framework offers a robust approach to enhancing risk assessment and analysis of retaining walls.