Transient Flow Behavior Caused by Long Foundation Pit Dewatering in a Leaky Confined Aquifer

Groundwater drawdown during dewatering of long excavations is influenced by cutoff walls and leakage from adjacent aquitards, yet their coupled transient effects are not fully represented by existing semi-analytical models. We develop a two-dimensional semi-analytical solution for constant-rate pumping in a leaky confined aquifer bounded by a partially penetrating cutoff wall. The formulation accounts for aquifer anisotropy, aquitard storage and vertical leakage, partial penetration of the pumping well, and groundwater exchange beneath the wall. The governing equations are solved using Laplace transformation and separation of variables; numerical Laplace inversion yields time-dependent drawdown. Model predictions are compared with finite-element results, a published non-leaky solution, and pumping test observations from a long excavation in Shanghai. The parameter analyses indicate that deeper wall penetration increases in-pit drawdown while slightly reducing drawdown outside the wall. Lower vertical-to-horizontal hydraulic conductivity ratios intensify the in-pit response. Reducing aquitard hydraulic conductivity or increasing its thickness limits leakage recharge and raises drawdown in both zones, whereas aquitard specific storage primarily influences the timing of the transient response. The results demonstrate that wall geometry and aquitard properties jointly control drawdown magnitude and evolution, and that the proposed solution can support preliminary assessment of dewatering schemes where two-dimensional flow is a reasonable approximation.