A comparative study of the different responses of circular and horseshoe-shaped tunnels to an advancing tunnel underneath Available to Purchase

Previous studies on tunnel interaction mainly focused on parameters such as cover depth, pillar depth and construction sequence with little attention given to the influence of tunnel shape. With discontinuous hoop stress distribution along the tunnel lining, non-circular tunnels are expected to respond to the construction of new tunnels nearby differently from circular tunnels. This paper investigates the effect of tunnel shape on multi-tunnel interaction by means of physical and numerical modelling. Two, three-dimensional (3D) centrifuge model tests were carried out simulating the existing circular and horseshoe-shaped tunnels. The test results were back analysed using PLAXIS 3D. An advanced hypoplastic constitutive model with small-strain stiffness was adopted for the numerical back analysis. Centrifuge test results show that the existing horseshoe-shaped tunnel experienced ∼ 20% more vertical elongation in the mid-plane than the existing circular tunnel. The measured and computed bending strains at the invert of the horseshoe-shaped tunnel were three times larger than those at the invert of the existing circular tunnel in the transverse direction. However, hoop stress along the tunnel lining in the existing circular tunnel was larger than that in the horseshoe-shaped tunnel.