Assessment of the Effect of Depth on Interaction between Single and Double-Tube Tunnels in Urban Areas using 3D Numerical Modeling

Evaluation of the interaction between new and existing underground structures is one of the most important problems in urban tunneling. In this paper, three-dimentional finite difference numerical model of single and twin tunnels in urban areas has been presented. The aim of this research was to evaluate the effects of changing the depth of excavating single tunnel, in constant horizontal distance, on the interaction of single and twin tunnels considering various criteria including forces and moments exerted on twin-tunnels lining and their safety factors, subsidence of ground surface and nearby buildings, excavation stability of single tunnel and stability of pillar lying between single and twin tunnels. The case study is related to single and twin tunnels of Tabriz urban railway, in northwest of Iran. Results indicated that increasing depth of single tunnel causes average safety factor of Sahand tunnel to decrease (6.52 to 6.35) and that of Sabalan to increase (6.78 to 7.02). As the depth of single tunnel increases, excavation stability of single tunnel increases and surface subsidence decreases. The stability of pillar lying between twin and single tunnels increases as the depth of single tunnel increases.