Analysis of Interaction Between Two Parallel Tunnels: Fid-Bau Portal

Analysis of Interaction Between Two Parallel Tunnels

R. E. Ranken / J. Ghaboussi

The finite element method of analysis was used to study the behavior and interaction of two circular and parallel tunnels. Depth of burial, tunnel spacing and construction sequence were the system variables considered in greatest detail. Throughout the investigation, which was restricted to two-dimensional analyses, the ground mass was assumed to be a continuous, isotropic and homogeneous medium with a free-field stress system corresponding to the self-weight of the medium and Ko = 0.5. Except for three elasto-plastic analyses, all of the analyses assumed linear-elastic stress-strain behavior for the medium. The simulated support conditions approximated the installation of the liner either right at the tunnel face or far behind the face. Depths of cover equal to one tunnel diameter and five tunnel diameters were considered. In one series of analyses it was assumed that both tunnels advanced together at the same rate. In addition, the position of liner installation was considered to be the same in both tunnels. Three pillar width to tunnel diameter ratios (W/D = 1.0, 0.5 and 0.25) were simulated in this series of analyses. In a second set of analyses the construction sequence was altered such that the face of one tunnel was far ahead of the face of the second tunnel. Here only one pillar width (W/D = 0.5) was examined. Tunnel I was simulated as having been lined right at the face, lined behind the face but ahead of Tunnel II, or not lined until after passage of Tunnel II. Tunnel II was assumed to have been lined either right at the face or far behind the face.