Analytical solution of pore pressure in seepage field of foundation pit with a sealed bottom under water level fluctuation

The pore pressure response of two-dimensional seepage field of a foundation pit with a sealed bottom under the condition of water level fluctuation is studied analytically. The soil around the pit is divided into several regions, and the excess pore water pressure response distribution in each region is expressed in the form of a series by applying the superposition principle and the separation variable method, and the coefficient matrix is solved by combining the inter-region boundary conditions and the continuity conditions to obtain the explicit analytical solution of the excess pore water pressure distribution of the two-dimensional seepage field in the pit with a capping layer under the fluctuation of water level. The results of the analytical solution are compared with the numerical results, and the correctness of the analytical method is verified. Based on this analytical solution, calculation formulae for the outflow ratio drop and water inflow caused by water level fluctuations are further provided. The sealing effect of the bottom layer and influences of the bottom layer thickness and permeability coefficient changes are discussed through a pit project example. The results show that the outflow ratio drop and single width seepage discharge are increased, but the rate of increase reduces as the bottom layer thickness decreases and the permeability coefficient increases.