Field observation of artificial recharge of confined water in first excavation case in Tianjin

By carrying out in-situ pumping tests in an excavation of Tianjin, hydraulic connection between the first and second confined aquifers is observed. Because the second confined aquifer isn't cut off by waterproof curtain, to reduce or eliminate the settlement of the key protected buildings induced by dewatering, the artificial recharge is applied during the process of excavation and dewatering in the pit. Five recharge wells are arranged around the protected buildings to recharge the confined aquifer using the urban water. The in-situ monitoring results show that the water volume recharged by a single recharge well can reach 24 m³/d to 72 m³/d and the water head can be raised as much as 6 m. The measured settlement of the buildings during excavation further shows that the variation of the settlement of the protected buildings almost simultaneously and directly relates to the fluctuation of the head of confined aquifer. It’s the first successful case of recharge of confined water in an excavation in Tianjin based on settlement control.