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Tunnel Forst

The subsoil is exclusively made up of quaternary deposits of the Rheingraben with fine sand, sand and gravel sand. They are loosely bedded down to a depth of 6 to 7 m, thereafter medium to densely compact. The groundwater extends to the ground surface. The horizontal degree of permeability of k = 3.4 x 10ˉ³ m/s is relatively high. Cut-and-cover construction with the required lowering of the groundwater would have represented serious meddling with the groundwater table of the immediate vicinity and further afield and was thus rejected. The Forst Tunnel was, first and foremost, built for ecological considerations rather than technical ones. If a surface route had been selected, the community of Forst would have separated from the neighbouring recreational area. The tunnel was created by cut-and-cover. The excavation was secured by an anchored sheet piling retaining wall and was divided by partitions. In order to dry out the excavation, vibration injection piles were installed to secure the base plate against uplift and subsequently the unreinforced base plate was put in position. The tunnel was executed in watertight concrete. The length of the blocks, which have no working joints, amounted to 8.80 m. The monolithic method of construction as well as the fact that only very minor crack widths resulted increase the prerequisites for watertightness considerably. The application of an anchored underwater base plate to avoid groundwater lowering was practised for the first time during the construction of the Forst Tunnel in Germany - and with great success. Since its completion, other structures have been built in accordance with this construction method.

 

  • Country: Germany
  • Region: Baden-Württemberg
  • Tunnel utilization: Traffic
  • Type of utilization: Main-line rail
  • Client: Deutsche Bahn AG
  • Main construction method: Open
  • Type of excavation: Cut-and-cover
  • No. of tubes: 1
  • Tunnel total length: 1726 m Tunnel, 1497 m trough cross-section
  • Cross-section: approx. 135 m²
  • Contract Volume: approx. 85 mill. DM
  • Construction start/end: 48 months