Analytical Solution for a Steady Seepage Field of a Foundation Pit in Layered Soil

Abstract

To reduce the negative influence of groundwater on foundation pit excavation and the surrounding environment, an analysis of seepage fields has become very important in deep excavation projects. However, the current studies on the seepage fields of foundation pits lack in-depth theoretical research, partly because the theoretical solution is complex and obscure, and the solution is limited to single-layer soil, which is difficult to apply to engineering practice. By using orthogonality and boundary conditions to construct nonhomogeneous equations, this study deals with the development of an explicit analytical solution for predicting stable seepage around a foundation pit in layered soil underlain by an impervious barrier and a constant water head maintained inside and outside the foundation pit. The validity of the analytical solution is checked by first reducing the proposed multilayered solution to that of a single-layered solution by treating the conductivity of the layers as the same and then comparing this solution with the hydraulic seepage situations predicted by the reduced model with corresponding values obtained from other analytical works. A numerical model is established using FLAC2D software to verify the solution proposed in this study and to obtain strong consistency. The solution is of a general nature and can account for the foundation pit width, the distance of the retaining wall from the impervious layer, the head difference, and the permeability variation in the layers of the soil. The study shows that flow to a multilayered foundation pit is sensitive to the width of the foundation pit, the embedded depth of the waterproof curtain, the thickness of the completely saturated soil up to the impervious barrier, and the total head difference. Furthermore, this study proves that the distribution of the conductivity in the layers plays an important role in determining the water head and the distribution of the streamlines. The results of this research could be considered in foundation pit design and water conservancy engineering practice.