Analysis of Mechanism of Water Inrush in Karst Tunnels

Abstract

In China, carbonate rocks cover an area of 3.443 million km squared, which consist of 36% of the nation's territory. It is not unusual to encounter karst related problems in tunnel construction. It is a difficult problem to build tunnels in complex karstified area. Strong and complex karstification makes it dangerous because water inrush is common during tunneling. About 50% of the built tunnels had the water inrush problems. The newly built Yuanliangshan Tunnel on Yu-Huai railway line crosses the karstified area, many times of water inrush occurred and caused big damage. Now, a railway line from Wanzhou to Yichang crosses the strong karstified area, there are 127 tunnels and most are karst tunnels, of which 10 are large karst tunnels and several tunnels such as Bieyancao and Qiyueshan tunnels had experienced water inrush. Thus, water inrush has become a big obstacle in tunnel construction in karst area. In this paper, the performance of karst cavities with high pressurized water are studied due to their possible dangerous and frequent burst or collapse. A model is developed to predict the critical thickness of the water-bearing rock between the karst rock cavity and the tunnel. Based on this model, the cause of the water inrush from Yuanliangshan Tunnel in Tongmangling section is analyzed. Proposed model can also predict the water inrush phenomenon. As another example, the proposed model is applied to forecast the water inrush of Qiyueshan Tunnel in order to ensure the safety in tunnel construction.