Seepage analysis in a fractured rock mass: The upper reservoir of Pushihe pumped-storage power station in China

A numerical simulation model of seepage in a fractured rock mass was constructed, based on the hydrogeological conditions of the upper reservoir of Pushihe pumped-storage power station in China, which is currently under construction. In addition, an analysis was conducted of groundwater movement in the reservoir-rock system, and calculations were made of the leakage rate and distribution of seepage under various operating conditions. During the simulation, the most important but most difficult problem was the determination of the hydraulic conductivity tensor of a fractured rock mass. This paper modifies the method of determining the hydraulic conductivity tensor, so that it not only reflects the permeability characteristics of the fractured rock mass, but also improves the calculation precision. The principal values and directions of the hydraulic conductivity tensor were first determined with a statistical method based on measurements of the spatial spreading of the fractures, and were then modified using estimates of isotropic hydraulic conductivity that were calculated by the Babushkin formula according to the water permeability rate from a field water-pressure test, and finally were verified using an inversion analysis with a mathematical model. The simulation results show that the total leakage rate is estimated to be 5832.92 m3/d, under the operating conditions of a normal pool level, and no anti-seepage treatment. Results of the analysis of various seepage-control scenarios suggest that the preferred scenario is grouting curtain only in the dam foundation, with the curtain depth 5 m below the line where the water permeability rate equals 3 Lu, thus reducing the leakage rate by 3571.27 m3/d. The above results provide a basis and reference for designing seepage-control structures and facilitating decision-making.