Analytical solution and application of unsteady flow model under suspended curtain

The combined dewatering measures of intercepting and drainage are mostly adopted the deep excavation of subway project constructed by seas or rivers. The groundwater around these deep excavation mostly exhibits unstable flow behaviors due to the influence of sea(river) water recharge. Therefore, a practical calculation model for pumping water from confined aquifer considering suspended curtain and fixed recharge is established. The drawdown solution in Laplace space is obtained by using Laplace transform and finite Fourier cosine transform, and inverted into the real space by using Stehfest numerical inversion method. Moreover, degenerate analysis and finite element numerical solution are applied to validated the correctness of the analytical solution. Finally, based on the analytical solution, the unstable characteristics of groundwater under deep excavation are analyzed and the following conclusions are obtained: at the later stage of pumping, after the groundwater seepage tends to be stable, the greater the insertion ratio of the water stop curtain, the greater the water level drop of the pumping aquifer in the foundation pit, and the water level drop of the pumping aquifer outside the foundation pit decreases with the increase of the insertion ratio of the water stop curtain; The closer the fixed recharge is to the foundation pit, the shorter the time for the water level of the pumping aquifer in the foundation pit to reach stability, and the smaller the water level drop after reaching stability; The water level drop of the pumped aquifer outside the foundation pit is significantly affected by the anisotropy of the aquifer. Meanwhile, a relative depth reduction ratio is proposed to divide the impact of fixed recharge into three zones: high impact zone, transition zone, and low impact zone. Corresponding design and construction suggestions are put forward for different affected areas to ensure the dewatering effect of the foundation pit.