Analytical scrutiny of loosening pressure on deep twin-tunnels in rock formations

Abstract Structual analysis of deep twin-tunnels is a cumbersome job due to the complex mechanism of tunnel-ground-tunnel interactions. This paper deals with the loosening pressure on the deep twin-tunnels. The deep twin-tunnel is divided into three patterns based on the different distributions of the failure zone. An analytical method is proposed to predict the surrounding rock pressure on deep twin-tunnels through the modification of the Protodyakonov's equilibrium arch theory (PEAT). The influences of the clear distance, reinforcement coefficient, excavation span and excavation height on the loosening pressure are discussed in some details. The obtained results by the proposed method are then compared with the in-situ monitoring data and a reasonably good agreement is achieved. The complementary studies suggest that the proposed approach is a trustable one for the preliminary design of deep twin-tunnels.