Field tests on groundwater recharge of deep excavations in Nantong water-rich sandy stratum

A series of field tests of single-well pumping and group-well pumping are carried out in Nantong water-rich sandy soil to study the change of hydraulic characteristics of different soil strata. The mechanism of dewatering-induced ground subsidence and relationship of soil restoration over time caused by water level recovery are further analyzed. The results show that: (1) In the water-rich sandy stratum with great depth, the groundwater changes quickly and its level can return to a steady state in a short time. However, the development of soil settlement changes slowly due to the characteristics of hysteresis. (2) The process of group-well pumping tests has a great influence on the phreatic aquifer (settlement of 37 mm), but a small impact on the confined aquifer (settlement of 6 mm). Moreover, it has little effect on the overlying soil strata in a short time. (3) In the artificial recharge tests, the groundwater level rises obviously. However, the phenomenon of soil restoration is subtle and shows the characteristics of unrecoverable plastic deformation. The plastic deformation of 20.2 mm in phreatic aquifer is greater than that of 2.9 mm in confined aquifer. (4) During the whole process, it is recommended to control the switching time of double-power supply in the phreatic aquifer within 7 min and that in the confined aquifer within 4 min. Additionally, the later recharge pressure should be preferably 0.08 MPa. In the protected district of sensitive buildings, pumping and irrigation should be integrated to minimize the deformation caused by precipitation.