Lining forces in tunnel interaction problems

Abstract

In big cities the construction of new tunnels in close proximity to existing ones is unavoidable given the densely and growing occupation of the subsoil. The interaction between tunnels in such conditions is well identified in the literature and has been thoroughly investigated in the past. However, most of those studies are focused on the effect of the ground conditions and relative position between tunnels on the ground movements and often disregard the impact induced by the second excavation on the lining forces of both tunnels. To provide further insight into this subject a numerical study of the sequential excavation of side-by-side twin tunnels is presented in this paper. The study also assesses the influence of parameters that have not been covered in the previous studies, namely the stiffness of the lining and the initial stress conditions. The results confirm that significant interaction occurs when the tunnels are spaced less than one diameter, where a considerable increase on both hoop forces and bending moments, particularly on the lining of the existing tunnel, is observed after the second excavation. For a spacing higher than two diameters the interaction between tunnels is almost negligible. The magnitude of the lining forces and of the interaction effects are also dependent of the stiffness of the linings and of the initial stress conditions.