Effects of granite stratum with different weathering levels on water discharge in metro tunnels

Abstract

This paper proposes a method for calculating the water discharge in metro tunnels considering limited drainage. With this method, groundwater resources and vegetation can be protected on the premise of ensuring the structural safety of tunnel linings. The water discharge in drainage-limited tunnels constructed through weathered granite was investigated. The water discharge characteristics were explored under different parameters of the shotcrete layer and grouting ring. The effects of the thickness and permeability coefficient of the weathered granite strata on the water discharge in the tunnel were discussed and the results were validated by in-situ monitoring of the water discharge. The results showed that the water discharge decreases with the increase in the thickness ratio of the grouting ring and shotcrete layer and with the decrease in the permeability coefficient ratio of the shotcrete layer and grouting ring. The water discharge can be effectively reduced by increasing the thickness or decreasing the permeability coefficient of the grouting ring. Once the ratio of the grouting ring to the thickness of the shotcrete layer exceeds 20, the water discharge no longer decreases significantly, and by tuning the parameters of the grouting ring, tunnel construction costs can be reduced without affecting the groundwater resource or vegetation around the tunnel. The proposed method can serve as a basis for regulating the water discharge in tunnels located in ecologically fragile regions.