Relationship between twin tunnels distance and surface subsidence in soft ground of Tabriz Metro - Iran

This paper presents a series of three-dimensional finite distinct element analyses carried out for line 1 of Tabriz metro tunnels. Interaction between these circular parallel twin tunnels excavated by an Earth Pressure Balance machine in a soft ground has been studied. The Influence of the distance between twin tunnels on the surface subsidence, bending moment and axial forces in the segmental lining of the first tunnel have been particularly, investigated. Advancing of the second tunnel affects the surface subsidence, bending moment and internal forces in the lining of the first tunnel. These effects relate directly to the width of the pillar separating the twin tunnels. It was found that the location of the maximum subsidence is offset from the centreline of the first tunnel. The offset increases with decrease in the distance between the tunnels. Also, moment and axial forces of the first tunnel decrease by increasing the space between the tunnels. The interaction between the tunnels has been quantified and classified in accordance with various tunnel distances.