Investigation on effect evaluation of seepage control system of large underground powerhouse of the Baihetan hydropower station

Abstract

The Baihetan Hydropower Station, situated in the lower reaches of Jinsha River in China, ranks as the second largest hydropower project. Effective seepage control in the underground powerhouse area is paramount due to the complex geological conditions on the left bank compared to the right bank. To assess the efficiency of the seepage control system, a combination of field measurements and numerical simulations was employed. In the session of field measurements, the characteristics of seepage field such as the groundwater level, hydraulic head, and leakage quantity in the impoundment process were analyzed. It became evident that the seepage patterns within the underground powerhouse were heavily influenced by geological structures, particularly the staggered zones C3 and C2, along with the columnar joint basalt. Notably, the leakage quantity of these areas rate considerably increased during impoundment, peaking at 1049.7 L/ min at the water level of 816 m in 2021. A finite element model with the seepage control system was developed based on the stable seepage theory, simulating the seepage field under two different water levels (816 m and 825 m).The numerical simulation results indicated that the grouting curtain and drainage hole arrays had a substantial lowering the groundwater levels. Comparing with the measurements, the inaccuracy of calculated total leakage quantity was 0.7 %, which was within the pumping capacity. The study provided a method of combining field measurement and numerical simulation to evaluate the effect of a complicated seepage control system for a large hydropower project. This method comprehensively revealed the seepage field of the underground powerhouse during the impoundment. It proved to have guiding significance for the operational stability of the hydropower station.