Seepage field analysis and evaluation of seepage control effect at the dam foundation of Baihetan Hydropower Station

With a large catchment area, stratified groundwater on the left and right bank, developed unloading fissures in the dam foundation rock, and prominent permeability anisotropy in columnar jointed basalt, the dam site of Baihetan Hydropower Station possesses complex seepage control measures. Moreover, the water head difference between the upstream and downstream can reach 235 m after impoundment, and thus, the seepage field of the dam site area will be extremely intricate. In this study, we analyzed the seepage field characteristics of the dam foundation during impoundment with field measurement data, and conducted numerical simulation of seepage field under normal water level condition with steady seepage calculation method. With the field measurement data and the numerical simulation results, we evaluated the performance of the seepage control system and revealed the movement process of the seepage flow in the dam foundation. The analysis results show that the impervious curtain can effectively stop the reservoir water from flowing to downstream side of the dam through the rock masses in the dam foundation, the drainage holes of the dam foundation can successfully mitigate the uplift pressure, and thus, the stability of the dam body has been guaranteed by the current seepage control system. Besides, driven by high water head difference, the reservoir water penetrates downstream through the deficient area of the impermeable curtain and flows along the micro-cracks developed in rock layers P2β32−2 and P2β32−1, then discharges through the drainage holes in the dam foundation.