Experimental study on seepage characteristics and water inrush of filled karst structure in tunnel

Taking Qiyueshan Tunnel as the engineering background, the three-dimensional model test system of tunnel water inrush and mud gushing was independently developed to study the structural instability characteristics and seepage laws of karst conduit fillings with different permeability coefficients. Then, the instability process of the filling, the evolution of water pressure, and the characteristics of the hydraulic gradient were analyzed. It is concluded that the fillings with different permeability coefficients show different instability characteristics, and the failure types of karst conduit filling are divided into sand inrush, water inrush, and mud inrush according to the instability characteristics of the filling. The pore water pressure at each measuring point in the filling material tends to decrease gradually along the direction of the confined water seepage. As the pressure of the confined water increases, the pore water pressure value of each measuring point increases gradually. And the higher the content of clay in the filling material is, the higher the maximum confined water pressure that the filling can bear when the filling material is unstable. The average hydraulic gradient in the filling increases with the increase of confined water pressure. The adjacent hydraulic gradient value increases with the increase of confined water pressure.