Jinping II Hydropower Station

located in Liangshan Autonomous Prefecture of Sichuan Province

is a highest water head and biggest capacity one at the in Yalong River. The underground powerhouse

the core of the project

is situated in right bank of V-shaped valley of the Yalong River. It meets the complicated groundwater seepage environment. For the safety of underground caverns

a reasonable layout of impermeable layer and discharge outlet is put forward based on the new design principle which is ponding first and discharge second

free drainage of high head wall

pumping of low head water

separating out water and inner water. Based on the result of 3D seepage numerical calculation of powerhouse region

the parameters of layer and discharge outlet system are also decided

which considers a rational safety scope. Practice of excavation of caverns proves that the design of seepage control and drainage system is reliable.