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The construction of the pilot tunnel with enlargement and test sections was carried out to more closely investigate the rock conditions and in order to prepare for the main drive through - in tunnelling terms - particularly tricky unleached gypsum keuper, which is prone to swelling when water is present and to undertake tests. Lot 1 (western side, Oberderdingen) Pilot tunnel The tunnel was first of all cut in the leached rock zone of the "Central Gypsum Horizon" in accordance with the shotcreting method. The inspection zone U1 had to be relocated in an actively swelling zone outside the tunnel cross-section owing to a lack of swelling activity. Tile static behaviour was tested on the tunnel cross-sections on a 1:2 scale along with the resistance principle as well as the method with yielding base support which was later selected for execution. Inspection zones U2, U3 In these zones, the gypsum level is located only a few metres above the tunnel roof. A partial disaggregation of the rock could not be prevented while driving the tunnel cross-section. This meant that water could possibly penetrate the unleached ground which was prone to swelling. Lot 2 (eastern side, Diefenbach) Pilot tunnel The first 200 m of the pilot tunnel was driven by the shotcreting method. Subsequently, compressed air was applied, corresponding with the lowering of the groundwater, for a TBM drive over approx. 1,200 m. Unreinforced extruded concrete was used to secure the tunnel lining. After arriving at the gypsum layer, the machine was dismantled and the remaining section cut protected by compressed air and advance grouting measures along the gypsum layer in accordance with the shotcreting method. Inspection zone U4 In this zone, the tunnel passes through the dipping gypsum layer in a protracted, looping section. The high groundwater level at the leached side and the ground prone to swelling on the unleached side meant that far-reaching sealing injections were necessary in this transition zone. Following successful sealing operations, both tunnels (Lot 1 and Lot 2) were connected with each other.


  • Country: Germany
  • Region: Baden-Württemberg
  • Tunnel utilization: Traffic
  • Type of utilization: Main-line rail
  • Client: Deutsche Bahn AG
  • Main construction method: Trenchless
  • Type of excavation: Roadheader/Drill-and-blast/Tunnel boring machine (TBM)
  • Lining: Shotcrete
  • No. of tubes: 1
  • Tunnel total length: 6756 m, incl. 655 m cut-and-cover
  • Cross-section: 153-191 m²
  • Contract Volume: 540 mill. DM
  • Construction start/end: 1986-1990 (4 years)
  • Opening: December 1990