Stability analysis of pile-stabilized slopes with cracks under groundwater level fluctuations

This study presents an analytical method for assessing the stability of pile-reinforced slopes with vertical cracks under fluctuating groundwater levels. A Fredlund-Xing based nonlinear shear strength model is developed for capturing the nonlinear behavior of soil strength and then integrated into a log-spiral failure mechanism with vertical cracks. The work-rate from soil weight is calculated using a layered integration method, accommodating nonlinear unit-weight variation. Applying the work-energy principle yields closed-form solutions for the required anti-sliding force, considering both pre-existing and formation cracks. The proposed method is validated against existing solutions (maximum relative error≤ 19.51%). Parametric analyses provide three key takeaways: 1) groundwater drawdown reduces the required stabilizing force by increasing matric suction, and optimal pile placement is near the slope toe; 2) anti-sliding force varies non-monotonically with crack depth and exhibits a critical threshold, which is substantially lowered by surcharge at slope crest, promoting deep-seated failure; 3) conservative estimation of anti-sliding force requires a soil-specific shear strength model: Vanapalli model for sandy soils; for fine-grained soils, Vanapalli model under high suction and Fredlund model under low suction; and Vilar model for clays and very fine-grained soils. These findings provide critical insights for slope reinforcement design under complex hydromechanical conditions.