Mechanical Behavior of a Double-Layer Supported Large-Span Tunnel Excavated in Squeezing Rocks Employing Stress Release Technology

Abstract

When excavating a large-span tunnel in squeezing rock, the tunnel support is subjected to significant loads. Therefore, the support structure must have enough stiffness and strength to withstand the pressure exerted by the ground. Various stress relief techniques can be used to reduce the ground pressure acting on the support and utilize the bearing capacity of the surrounding rock. One such technique is Deformation Reserved (DR). It involves reserving space outside the excavation boundary or between the two support layers. The proposed solution for the interaction between the double-layer tunnel support and the surrounding rock takes into account the excavation process and stress relief. The expressions for stress and deformation of the tunnel support and surrounding rock are provided in an elastoplastic solution. Parametric studies were conducted to investigate the effectiveness of a double-layer support structure with stress relief techniques. The monitoring data from the Lianchengshan Tunnel were compared with the proposed analytical solution. The results indicate that a larger reserved deformation behind the outer layer support is much more beneficial to tunnel stability when the total reserved deformation is constant. The ground pressure will be significantly reduced, thereby decreasing the force on the inner layer support.