Mechanisms of pile-soil stress and deformation in excavations under the coupled effects of excavation disturbance and extreme rainfall infiltration

Under the increasingly frequent extreme rainfall events, deep excavations are subjected to complex coupled effects of excavation-induced disturbance and rainfall infiltration, making it essential to clarify the deformation mechanisms of surrounding soils and retaining structures. In this study, a typical metro foundation pit in Zhengzhou was selected as the research object. By integrating field monitoring data with ABAQUS finite-element simulations, the deformation response and mechanical evolution of the pile-soil system under the combined influence of staged excavation and extreme rainfall infiltration were systematically investigated. The results indicate that rainfall infiltration leads to significant pore-water pressure accumulation, while the downward migration of the wetting front continuously reduces the effective stress and shear strength of the mid-to-deep soils. This process weakens the passive resistance at the pile toe and induces the downward movement of the primary deformation zone. The bending moment distribution of the retaining piles evolves from a "coexisting positive-negative moment" pattern to a "positive-moment dominant" mode, and the horizontal displacement at the pile toe changes from negative to positive, revealing a coupled mechanism involving deep-soil softening and arching loss. A mechanical chain of rainfall infiltration, pore-pressure evolution, stress redistribution, and pile-soil deformation is established to explain how extreme rainfall amplifies excavation-induced effects through dual pathways of mid-to-deep soil softening and accelerated seepage. Based on these findings, a prevention framework of source reduction, structural enhancement, and process control is proposed to improve the safety and resilience of deep excavations under extreme climatic conditions.