A new numerical method for the analysis of monolithic seepage problems with complex drainage systems in a groundwater recharge area for a hydropower station in China

After construction of a dam impounding water in a reservoir, a monolithic seepage field develops in the surrounding rock mass. Here, a new finite element method is proposed for determining the shape and characteristics of the 3D monolithic seepage field including the free surface, considering complex drainage systems consisting of densely-spaced drainage holes and drainage galleries. To this end, the previously proposed virtual flux method is improved by a refined numerical integration scheme and a regularized Heaviside function for distinguishing the subregions below and above the free surface within a particular finite element. Leakage and overflow drainage holes are modeled as internal boundaries. The proposed numerical method is verified by an academic example, for which the analytical solution is available. Finally, the numerical simulation of the seepage field developing in the vicinity of a high dam and underground power house, constructed in the context of a hydropower plant project in China is used to show its application to a problem in engineering practice.