Environmental effects of confined aquifer dewatering for cut and cover tunnels in floodplain areas of Yangtze River

Confined aquifer dewatering for cut and cover tunnels in the floodplain areas of Yangtze River characterized by complicated geological condition and high confined water level may result in considerable ground settlements, which may potentially cause structural damages and losses of life and property. Aiming at this issue, the finite element model for the confined aquifer dewatering is developed based on the southern part of a cut and cover tunnel of the Jiangyin-Jingjiang Yangtze River Tunnel Project, and the characteristics of drawdown, ground settlement and incline of a sensitive villa district are analyzed. The effects of various designs of curtain on the ground settlements are also studied. It is found that the settlements induced by the confined aquifer dewatering cannot converge fast. The maximum settlements of the villa district for 10, 30, 60 and 120 days of dewatering are 2.5, 4.3, 5.4 and 6.1 cm, respectively. The inclines converge faster with the maximum value of 0.0002, which meets the requirements of China's standard. The altered curtain design can reduce the maximum settlement in the villa district by 63.5%. Cutting off the second confined aquifer in the mainline can further reduce the maximum settlement with the highest efficiency.