Reverser at Matzleinsdorfer Platz: adapting the tunnelling concept to modified subsoil conditions

According to the tender planning for construction of the reverser at Matzleinsdorfer Platz, a tunnelling concept with inclined side wall drift was envisaged. The geological/hydrogeological forecast model on which this approach is based shows a water‐bearing Miocene coarse‐grained stratum in the floor area of the tunnel. To alleviate the pressure, groundwater‐lowering measures were planned. Owing to the significant differences in the effectiveness of the lowering wells and difficulties encountered when manufacturing the horizontal filter wells, there was some doubt as to whether this objective would be achieved at all. Consequently, the tunnel driving concept was changed to a system with pilot tunnel which is subsequently widened to the standard cross‐section of the reverser. By using a flexible arrangement of vertical wells which were drilled from the pilot tunnel, it was possible to satisfy the prerequisites for safe tunnelling. This article describes the decision‐making processes involved in the replanning, geotechnical challenges and advantages of implementing the modified groundwater‐lowering and tunnelling concept.