The High Speed Line (HSL) between Amsterdam and Brussels is not yet in operation and there are plans to cross this railway track by local roads and motorways. Movares has carried out a global research projects over infrastructures crossing an operational HSL. One of these research projects concerned the crossing the HSL by two large shield tunnels (15 m diameter) without generating any track deformations through tunnelling. An option to achieve this is to construct a “support bridge” i.e. a concerte plate to avoid local settlements of the railway track. The purpose of this support bridge is to carry the HSL track over the route of both shield tunnels free from eventual settlements. Figure 1 gives a 3D-view of the HSL and crossing tunnels. The global dimensions of the support bridge were calculated with the Plaxis 3D tunnel program in an early stage of design. This article gives a short description of the 3D Plaxis model, the model difficulties and calculation results.