Influence of artificial recharge in a phreatic aquifer on deep excavation dewatering: a case study of Dongguantou Nan Station in Beijing, China

Dewatering in deep excavation projects induces groundwater-level drops and the loss of groundwater resources. A series of multi-well pumping-recharge tests were carried out in a phreatic aquifer in Beijing (China) to study the feasibility and effectiveness of artificial recharge applied to dewatering projects and to understand the influence of artificial recharge on deep excavation dewatering especially. During the tests, the abstraction and recharge quantity were almost equal. The abstraction was positively correlated with the injection. Under the conditions of significant groundwater-level difference and excellent hydraulic conductivity in the gravel strata, the injected water mainly seeped towards the excavation sites and quickly induced an increase in abstraction quantity. For example, to maintain the groundwater level in the excavation pits at 15 m above mean sea level, the water abstraction rate from the pits increased by 21,702 m³/day (i.e., increased rate of about 32%) compared with the corresponding case without recharge. The results show that it is feasible to conduct artificial recharge to infiltrate all the pumped water into the pumped aquifer and simultaneously maintain the excavation pits in dry workable conditions; artificial recharge has the advantage of mitigating groundwater overexploitation and helping the goal of sustainable use of water resources. To ensure the successful operation of the pumping-recharge system, an analytical method was proposed to predict the discharge rate (or quantity) under the combination of pumping and recharge based on steady-state and Dupuit assumptions. The usefulness of this method was demonstrated with data from field tests.