Experimental study on artificial recharge of second Tianjin silt and silty sand micro-confined aquifer

The recharge measures are used to try to control the settlement and head down of the confined aquifers caused by the pumping of the foundation pits in Tianjin, Shanghai and other regions. However, the researches on the theory of recharge are still deficient, and the feasibility of recharging in the micro-confined aquifer of silt and sandy silt is also urgently needed. Therefore, a series of single-well recharge tests, group-pumped and group-recharge tests and double-combined recharge tests near a subway foundation pit project in Tianjin are carried out. The test results show that it is feasible to recharge in silt and fine sand as the main component of the soil layer, and the pumping theory can be used to predict the change of the water level in confined aquifers caused by recharge in practical engineering within a certain range. The hydrogeological parameters obtained by the pumping tests can be used to predict the rise of the water level of the recharge, but at the same flow rate, the uplift of the water level generated by recharge is significantly greater than the drawdown of the water level caused by pumping within the distance from the center well (about 5 ~ 7 m). The pressurized recharge can improve the efficiency remarkably. The amounts of recharge and pumping at a similar level can effectively control the settlements of the surrounding surface and buildings. The surrounding surface subsidence has a rapid development trend when the recharge is stopped. In practical engineering, in order to avoid such a settlement trend with rapid growth, the recharge time is properly extended after pumping is stopped, the amount of recharge is gradually reduced, and the groundwater level is gradually stabilized so as to avoid the rapid development of settlements at the end of pumping and recharge. The twin-well combined recharge technique can be used to control the decline of the water level of aquifers caused by the discharge of the recharge well.