Three-dimensional analysis of tunnel intersections for a train tunnel under Stockholm

The Citybanan commuter train tunnel will comprise a 6km long, double-track train tunnel to be constructed in rock under Stockholm City. In this paper, analysis of the intersections between the planned train tunnel and so-called "energy tunnels" is described. The objective of this analysis was twofold: (i) to predict deformations and stability of the energy tunnels caused by excavation of the train tunnel, and (ii) to determine required rock reinforcement for the train tunnel. Analysis was conducted primarily using the three-dimensional finite difference program FLAC(3D). The analysis results showed that only minor deformations can be expected in the energy tunnels due to the excavation of the train tunnel, and that the overall stability of the tunnels was satisfactory. Furthermore, the results could be used to confirm a proposed rock reinforcement scheme for the train tunnels, thus securing the stability of the load-bearing structure for the rock tunnel.