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Kappler Tunnel, B 31, Transitway through Freiburg

As part of the building of the new B 31 within the Freiburg city boundaries, the 4-lane road tunnel on the B 31 is being created by cut-and-cover. This method was chosen because there is room to set up an excavation and the distance to buildings and the height of the groundwater level permits the groundwater to be lowered. Geologically speaking, the tunnel is located in the gravel layers of the Dreisamtal valley. The groundwater level is largely to be found some 1.20 m above the tunnel base or even beneath the base in part sections. The Berlin construction method cannot be applied when buildings are in the immediate vicinity of the excavation. In such cases, either concrete underpinning with high pressure grouting or a bored piling wall is executed. ln addition, the crossing of a road with a level crossing immediately adjoining it and 2 drains crossing the tunnel with diameters of 1 ,600 and 1 ,800 mm have proved to be very tricky. ln this connection, the block distribution had to be altered in such a way on account of the constricted conditions and the need to guide traffic that inclined block joints were produced. A formwork car is being used for this tunnel. Only special cross-sections, e.g. in the vicinity of emergency bays are shuttered by conventional means. The blocks (12.50 m long) are concreted in one go, resulting in 645 m³ being concreted in 1 day. Following initial difficulties, the weekly block schedule was adhered to. The tunnel is being provided with 2 sub-stations. The main service station is located in the Schützenallee Tunnel. There are 2 emergency stairway buildings and a pump station. The safety installations comply with the RABT. A pure longitudinal ventilation system is foreseen.


  • Country: Germany
  • Region: Road tunnel
  • Tunnel utilization: Traffic
  • Type of utilization: Road tunnel
  • Client: Bundesrepublik Deutschland, Straßenbauverwaltung Baden-Württemberg
  • Consulting Engineer: Regierungspräsidium Freiburg
  • Contractor: Ed. Züblin AG, Dyckerhoff & Widmann AG, Philipp Holzmann AG
  • Main construction method: Trenchless
  • Type of excavation: Cut-and-cover
  • Lining: In-situ concrete
  • No. of tubes: 1
  • Tunnel total length: 1250 m
  • Cross-section: 26 t
  • Contract Volume: 53.0 mill. DM
  • Construction start/end: 1997-2001 (4 years)
  • Opening: end of 2001