Prediction Method for Land Subsidence Induced by Foundation Pit Dewatering under Complex Conditions

［Objective］To study the land subsidence variation patterns induced by foundation pit dewatering under complex conditions, the deep foundation pit project at Nanjing Metro Line 5 Airport Road Station is taken as a case study to predict the land subsidence caused by foundation pit dewatering. ［Method］Field pumping tests and theoretical analysis are employed to analyze the land subsidence patterns induced by foundation pit dewatering. Single-well and multi-well pumping tests are conducted. The single-well pumping tests provide data on land subsidence patterns and dewatering influence radii for different soil conditions, while the multi-well pumping tests reveal the shapes of dewatering funnels across four typical cross-sections. A land precipitation subsidence prediction formula is derived using the subsidence consolidation equation tailored to the project conditions. The theoretical land subsidence values predicted by this formula are compared with field-monitored data to verify its applicability. ［Result & Conclusion］The influence radius of single-well pumping increases with permeability coefficient and dewatering depth, reaching about 5 meters in low-permeability soil and up to 20 meters in high-permeability soil in this project. The shape of the precipitation funnel follows an exponential curve, and land subsidence deformation is greater adjacent to the dewatering well. Land subsidence induced by dewatering rapidly decreases with distance increasing from the well.