Twin Tunnel Interaction: Surface and Subsurface Effects

Abstract

This article presents the results from 13 plane strain, coupled consolidation, non‐linear finite element analyses of twin tunnel construction. There are two sets of analyses, the first models two tunnels running parallel side‐by‐side, and the second one above the other (piggyback). The spacing between the tunnels is varied so as to ascertain the zones of influence, and the time between the construction of the two tunnels is varied to establish the influence of prolonged consolidation or swelling. The results present the expected modification to the settlement profile above the second of two close tunnel excavations, and the expected distortion induced in an existing tunnel lining when an adjacent tunnel is excavated. Field data, where available, are presented to support the magnitudes of the interactions being predicted numerically. It is concluded that the relative position (above, below, or to the side) and the physical spacing of the tunnels has a significant effect on the surface settlement profile due to the second tunnel, and on the response of the first tunnel lining to excavation of the second tunnel. The length of rest period has a negligible effect on these interaction effects.