Development and experimental validation of analytical models for water and mud inrushes through a filled karst conduit

Water or mud inrush has become a common geological disaster during tunnel construction in karst areas. To study forming process and mechanism of water and mud inrushes through a filled karst conduit, water inrush and mud inrush model tests were carried out with a self-developed 3D model test system. The results show that the forming processes of water inrush and mud inrush have different forming modes. For water inrush, the forming process follows: flowing instability of filling material particles—formation of water inrush channel—water inrush occurring; while for mud inrush, the forming process follows: stability—sliding instability of the whole filling material suddenly—mud inrush occurring. Accordingly, a local instability model of critical hydraulic pressure causing water inrush and an integral sliding instability model of critical hydraulic pressure causing mud inrush were established respectively. The two analytical models reveal the mechanism of water inrush and mud inrush experiments to an extent. The calculated critical hydraulic pressures for water inrush and mud inrush are in good agreement with the test results. The distinguishment of water inrush and mud inrush through a karst conduit was discussed based on the critical hydraulic pressure and the evolution law of seepage water pressure in tests, and a criterion was given. The research results might provide guidance for the forecast of water and mud inrush disasters during the construction of tunnels in karst area.