Control settlement of recharge in ultra-deep excavations under partial block effect of aquifer

In coastal cities in China, taking Tianjin for an example, the pressure aquifer is rather thick and buried deep. Cutting off all the aquifer will lead to high construction cost. Therefore, the suspended water-stop curtain is often adopted, in which the water level outside the excavation is inevitably influenced by dewatering. To protect building safety, the recharge is often introduced to control settlement. An analysis is given based on the drawdown and ground surface settlement data monitored during dewatering and recharging in the excavation of a station of Tianjin Rail Transit line 6. After the recharge is fully started, the water level of the neighboring area remains stable, and so is the development of ground surface settlement. The water level near the recharging area rises quickly, which is related directly to the amount of recharge. The ground surface settlement is recovered to a certain extent after starting recharging, but with certain delay. The expected recharge protection can be achieved. Recharging is kept during pit excavation and change in the pressure aquifer and ground surface settlement regularly is monitored. Upon exceptions, the amount of recharge is gradually increased to avoid change of ground surface settlement or even differential settlement of buildings caused by sudden change in the water level.