Analytical solution and application of unsteady flow model under suspended curtain

The deep foundation pits of nearshore subways mostly adopt the dewatering measures of cutting water and draining, and the groundwater around the foundation pits shows unstable flow behavior due to the influences of seawater recharge. Therefore, a mathematical model for the pumping of confined aquifer in a foundation pit under suspended water curtain and fixed recharge is established. The Laplace transform and finite Fourier cosine transform are used to obtain the solution of the water level drop in the Laplace space domain, and then the analytical solution is obtained by using the Stehfest numerical inversion method in practical space. Finally, the correctness of the degradation solution and numerical simulation are verified, and the influencing factors are discussed. The conclusions are drawn as follows: (1) At the later stage of pumping, after the underground seepage tends to be stable, the larger the insertion ratio of the waterproof curtain, the greater the depth of the water level of the pumped aquifer in the pit, and the deeper the water level of the pumped aquifer outside the pit decreases. (2) When the fixed recharge is closer to the foundation pit, the shorter the time for the water level of the pumped aquifer in the pit to reach stability, and the smaller the water level drops after reaching stability. (3) The drop in the water level of the pumped aquifer outside the pit is obviously affected by the anisotropy of the aquifer. At the same time, a relative depth ratio is proposed to divide the impact of fixed recharge into three zones: high impact zone, transition zone and low impact zone. The corresponding design and construction plans are proposed for different zones to ensure the dewatering effects of the foundation pit.