Control and Prevent Land Subsidence Caused by Foundation Pit Dewatering in a Coastal Lowland Mega City: Indicator Definition, Numerical Simulation and Regression Analysis
Abstract Coastal mega cities are often commercial centers because of convenient traffic. Safe elevation above sea level is vital for their sustainable development. Global climate change and sea level rising increase flood risk especially in the lowland subsidence area. Shanghai of China was selected as research background. Although groundwater exploitation had been strictly restrained to control land subsidence and reserve safe elevation, lowering groundwater level during underground excavation cannot be avoided. Foundation pit dewatering (FPD) was intensively performed in underground exploitation during urbanization and city renewal. The FPD settlement accelerated land subsidence. Controlling FPD subsidence was urgent. Normally, the maximum horizontal influence radius of foundation pit excavation was less than three times excavation depth (H), and the 3H settlement was only caused by the FPD. The 3H maximum settlement was defined as the evaluating indicator of FPD land subsidence, and the corresponding 3H drawdown was defined as the control indicator of land subsidence. The FPD conceptual models were established on the basis of estimation and investigation of foundation pit information, including pit area, pit shape, pit depth, and curtain depth. Numerical models were established and a total of 5650 FPD numerical simulations were performed to investigate the land subsidence and FPD drawdown. Multi-factor regression analysis was conducted to obtain relations between land subsidence and FPD drawdown. Regression models were established between the 3H drawdown and the shape, area, depth, and curtain depth of foundation pit on the basis of the numerical simulations. A typical example introduced to verify the regression models. The regression models were used to manage the FPD land subsidence by controlling the 3H FPD drawdown. The results can provide reference for the land subsidence control in a coastal lowland city.