A semi-analytical solution for seepage field and soil deformation induced by coupled pre-excavation dewatering and groundwater recharge with a suspended waterproof curtain considering delayed phreatic surface response

Abstract

Accurate prediction and effective control of soil deformation induced by pre-excavation dewatering are essential for construction safety in underground space development. However, the coupled effects of suspended waterproof curtains and external groundwater recharge on drawdown and soil deformation in unconfined aquifers remain unclear, particularly considering the delayed response of the phreatic surface. This study develops an improved theoretical model to characterize soil deformation induced by pre-excavation dewatering and external recharge under plane strain conditions, explicitly considering a suspended waterproof curtain and the time-dependent behavior of the water table. A semi-analytical solution is then derived using integral transform techniques and verified through laboratory model tests, degradation solutions, and numerical simulations. Parametric analyses indicate that prolonging time required for the groundwater level within the pit to reach the target value can substantially decrease soil settlement before excavation, which has minimal effect on the final steady-state settlement. Increasing the horizontal distance between recharge wells and the foundation pit mitigates far-field drawdown but may increase soil settlement within the pit, whereas longer well screens enhance phreatic surface recovery near the excavation. Furthermore, increasing the penetration depth of the waterproof curtain and appropriately scheduling the initiation of recharge wells can effectively limit external groundwater inflow, thereby reducing groundwater drawdown and soil settlement outside the foundation pit. Specifically, increasing the penetration depth of the waterproof curtain from 6 m to 12 m reduces internal settlement by 6.7% and external settlement by 77.9%, suggesting a stronger mitigation effect on the external side. These findings not only extend existing theoretical models by explicitly incorporating the coupled effects of suspended waterproof curtains and external recharge wells with delayed phreatic surface response, but also support and broaden prior findings by demonstrating how recharge design parameters and initiation timing critically govern drawdown and soil deformation in deep excavations.