Fully Coupled Numerical Analysis of the Impacts of Diaphragm Wall Leakage in Ultradeep Excavation

In Shanghai, China, where soft clays are abundant in groundwater, the rapid exploitation of ultradeep underground space poses significant attendant risks for groundwater control. Leakage through diaphragm walls in deep excavations is a potential risk, particularly when the structural integrity of the wall is compromised. However, the influence of such leakage on excavation deformations and soil responses remains poorly understood. In this study, a series of three-dimensional numerical analyses were conducted using a fully coupled method to investigate leakage-induced adverse impacts associated with an ultradeep excavation. The numerical model was validated by comparing calculated deformations with field monitoring data. Leakage in the diaphragm wall was subsequently simulated at certain stages during construction. A comparison between leaky and nonleaky cases was conducted, focusing on the wall deflections, ground settlements, pore pressures, stress paths, and stress distributions. Furthermore, in-depth parametric analyses were conducted to assess the hydraulic conductivity of the leaky zone and the soil layer where the leakage occurs. Results indicate that major leakage could increase wall deflection by 30% and ground settlement by 26% compared to the nonleaky case. Soil responses, including pore pressures and stress paths, are highly dependent on the hydrogeological properties of the soil layers and on dewatering activities. The magnitude of the impact of leakage is strongly influenced by the hydraulic conductivity of the leaky zone and the soil layer involved. The additional construction of a trench-cutting remixing deep wall curtain outside the diaphragm wall serves as an effective mitigating measure against excessive deformations caused by leakage through the diaphragm wall. It is therefore recommended as a precaution or countermeasure for addressing groundwater problems in similar geological settings.