Characteristics, challenges and countermeasures of giant karst cave: A case study of Yujingshan tunnel in high-speed railway

Abstract

Karst landforms were widely distributed all over the world, and they were mainly distributed in the Southwest and Southeast regions in China. However, tunnel construction in giant karst caves was rarely studied. In recent years, Yujingshan tunnel of Chengdu-Guiyang high-speed railway in Yunnan Province had encountered the largest karst cave in history of Chinese railway construction. This paper reported the hydrological and geological conditions of this case, as well as relationship between karst cave and tunnel, and compared it with the other three giant karst caves encountered in railway construction, and systematically analyzed the challenges it brought to tunnel construction, and put forward the corresponding countermeasures. Furthermore, in-situ monitoring results of the layered settlement of tunnel bottom and the crown settlement and horizontal convergence of tunnel in giant karst cave were analyzed. The results showed that the challenges mainly included: (a) huge scale of karst cave, (b) poor stability of cave wall, (c) poor stability and complex composition of filling content, (d) complex underground river and channels; the countermeasures mainly included: (a) backfill of cave, (b) roof reinforcement of cave, (c) both sides and the bottom reinforcement of tunnel, (d) diversion and closure of underground river, (e) bridge in the tunnel, (f) bench cut method. The feedback of in-situ monitoring results demonstrated the effectiveness of countermeasures. This case study can provide experience for construction of similar tunnels in giant karst caves.