Investigation of Seepage Behavior and Structural Stress Evolution Mechanisms in Karst Tunnels under Water-Rich Conditions during Operation

Utilizing a self-developed indoor model testing system for karst tunnels, the influence mechanisms of cavity location and water pressure on the water pressure distribution behind the tunnel lining, surrounding rock pressure, and lining stress were investigated. Furthermore, the impact patterns of cavity location and water pressure on the development of plastic zones in the surrounding rock of karst tunnels were determined, and the effect mechanism of the net distance between the cavity and the tunnel on structural stresses was revealed. Key findings indicate that: The presence of a cavity induces a distinctive “maple leaf” pattern in the Mises stress distribution on the tunnel lining section; Under identical water pressure, the Mises stress at a specific monitoring point on the lining is most significantly affected when the cavity is located at the tunnel crown, with minimal impact when it is at the tunnel invert; Under water pressure, the deformation curve of the tunnel support structure exhibits a generally “concave” shape, with the indentation directed towards the cavity center. This phenomenon intensifies with increasing water pressure and higher relative cavity positions; The influence mechanism of water head height on the lining axial force is complex, necessitating particular attention to the bearing capacity of the tunnel invert structure; The effect of water head on surrounding rock pressure follows a distinct pattern, and its analysis must account for the evolution characteristics of the rock mass structure under dynamic pore water pressure conditions.