Characteristics, numerical analysis and countermeasures of mud inrush geohazards of Mountain tunnel in karst region

The excavation of tunnels in karstic rocks inevitably intersects with karst caves even with reasonable geological survey and alignment design. The filler in karst caves directly affect the harmfulness of mud inrush geohazards to tunnels. Therefore, it is essential to understand the properties and failure characteristics of the filler in karst caves before treating karst caves. Based on a tunnel mud inrush case in Guangxi Province, China, failure characteristics and mechanism of clay filler in karst cave were analyzed. Besides, geological survey and geological prospecting indicate that the clay filler was formed by the deposition of surface clay entering the karst cave from the cracks of rock mass. The failure evolution process of clay filler was demonstrated based on discrete element method. The numerical simulation results show that excavation induced sliding force and insufficient shearing strength of clay were the mainly triggering of instability of clay filler in the karst cave. Advanced grouting, construction method improving were used to prevent mud inrush from bursting again and achieved satisfactory reinforcement effect. The lessons and analysis results in this case has reference value for the prevention of tunnel mud inrush in karst area.