Mechanical Response and Health Monitoring of Deep Excavations Under Extreme Rainfall

Real-time monitoring and early warning of foundation pits are critical for geotechnical safety. However, the rainfall-induced hydro-mechanical coupling effects on water-rich sandy excavations remain poorly understood. The impact of rainstorms on excavation stability demands urgent investigation. This study examines the response of a deep excavation at Beijing Daxing Airport during the “31.7” extreme rainfall event using a multi-sensor monitoring network and numerical simulations. Results reveal that excavation-induced displacement features a neutral point at 0.4–0.6H (H = slope height), with retaining pile displacements reaching 0.14%He (He = excavation depth). Extreme rainfall events elevate the groundwater table, triggering a rise in pore-water pressure within the soil mass. This process can induce excessive displacement in the excavation, posing a substantial threat to its overall stability. It is recommended to set the critical groundwater rise threshold for Beijing at 15% of the slope height (H) and to provide a 20% axial load-bearing safety margin for support systems in rainfall-prone areas. The safety threshold established in this study will serve as a scientific basis for early warning systems of excavation safety during extreme weather events.