Stress disturbance induced by twin-tunneling in sandy ground considering soil arching effect

Due to space constraints in urban areas, metro tunnels are typically constructed in pairs, with a small clearance. The interaction between twin tunnels leads to a significantly more complex ground deformation and stress distribution than that observed in a single tunnel scenario, particularly if the tunnels are excavated in sequence. A series of physical model tests were conducted to investigate soil deformation and stress disturbances caused by the excavation of twin tunnels. The test results indicate that the interaction between the twin tunnels was observed. Due to the soil arching effect, the excavation of Tunnel 2 increases the soil stress acting on Tunnel 1. An analytical method was proposed to determine soil stress considering the soil arching effect and the interaction between twin tunnels. The method categorized the relative locations between twin tunnels into non-influenced, partially influenced, and fully influenced scenarios. For non-influenced and fully influenced scenarios, the soil stresses above twin tunnels were calculated based on a symmetric major principal stress trace. For the partially influenced scenario, however, the soil arch above Tunnel 2 was asymmetric due to the interaction, and the stress distribution was obtained based on a new asymmetric major principal stress trace. The soil stress on Tunnel 1 was influenced by the load transferred from Tunnel 2 and calculated based on the force equilibrium. A comparison of the analytical and test results indicates that the proposed method effectively predicts the soil stress in the cover layer above twin tunnels excavated sequentially, considering the interaction and soil arching effects.