Field tests of pumping-recharge technology for deep confined aquifers and its application to a deep excavation

Abstract

The execution of deep excavation above confined aquifers asks for dewatering measurements to reduce the hydrostatic pressure so that the safety of the deep excavation can be assured. Dewatering will inevitably cause deformations in the surrounding strata. To reduce the dewatering-induced strata movement, an innovative pumping-recharge technology has been developed in which the dewatering is carried out in the excavation and the recharge is conducted near the protected facilities. However, the capacity and efficiency of this technology in deep confined aquifers need to be further investigated. This paper presents two in-situ pumping-recharge tests in a deep confined aquifer under a deep foundation pit. The feasibility of artificial recharge in the deep confined aquifer has been verified by conducting a single-well pumping and multi-well recharge test with different discharge and injection rates. Then a multi-well pumping-recharge test was carried out in accordance with the requirement and circumstance of construction to evaluate the capacity and efficiency of recharge in controlling the drawdown and ground settlement. The results showed that multi-well recharge could form a water curtain which has a water-proof function to reduce the groundwater drawdown. Meanwhile, by controlling the groundwater head of the confined aquifer during the recharge, the pumping-induced settlement of the surrounding area can be reduced or even eliminated. The pumping effect in the pit would be affected by the recharge around the protected facilities, so it is necessary to take in-situ pumping-recharge tests to determine the layout of wells and the discharge and injection rate. Finally, the artificial recharge was applied to the construction of a deep excavation in Shanghai, and the drawdown and the ground settlement around the protected buildings were effectively controlled by recharge.