High Water TableThe key challenges

High Water TableThe key challenges in building this pedestrian tunnel were the high water table created by the close proximity of the Danube River and addressing the need to prevent interruption of traffic flow on the street between the buildings. The street is both a major thoroughfare for cars as well as a street car line. The tunnel needed to be water tight to create a comfortable pedestrian space and the traffic needed to be maintained throughout the construction phase.The design team settled on the use of both cast-in-place and precast sections to create the tunnel. Precast was used below the road surface itself to speed construction and thus reduce the time that the full road surface was closed. Both parts of the tunnel had similar dimensions utilizing 20 cm (8 inch) thick walls and ceiling with a 40 cm (16 inch) thick base slab. The base slab was thickened to support the tunnel and overhead loads as well as to provide ballast to keep the tunnel from floating in the high water table environment.