Model test of the tunnel subjected to high water pressure in Jinping Second Cascade Hydropower Station, China

In the area with high groundwater pressure, grout curtain is often adopted to reduce the water pressure on tunnel lining. A series of model tests for the diversion tunnel of the Jinping Second Cascade Hydropower Station, China, is designed to study the effect of grout curtain. The impact of the thickness of grout curtain, permeability of grout curtain, internal water pressure and drainage inflow on the distribution of water pressure are discussed. The results indicates that under un-drained condition, water pressure is equal to hydrostatic one no matter grout curtain is selected or not, water pressure under drained condition is far less than that of un-drained condition, drainage in tunnel can reduce tunnel water pressure effectively. For same inflow, both increasing of thickness and decrease of hydraulic conductivity of grout curtain can reduce water pressure effectively. For the same water pressure, the smaller inflow of grout curtain, the less volume of water to be discharged. The impact of hydraulic conductivity of grout curtain is more obvious than that of thickness. With increasing of internal water pressure, the water pressure of grout curtain increases too, and the water pressure increases nearly linearly. The proposed thickness of grout curtain for the diversion tunnels is 16 m.