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Hornberg Tunnel

It was decided to build a bypass with the 1.8 km long Hornberg Tunnel at its core in order to decrease through traffic in the town of Hornberg on the B 33. The tunnel corresponds to the specifications laid down in the RABT 2003. It has been provided with 5 escape galleries, with the central one designed for traffic. A ventilation system with smoke extraction was selected above an intermediate ceiling on account of the tunnel's total length of 1,884 m. The intermediate ceiling is 1,409 m long and possesses 1.75 x 1.75 m² exhaust ports set 75 m apart. The roughly 50 m long ventilation centre is located at the north portal. The excavation began on the northern side on April16th, 2002 and the 1,804 m section was driven by mining means within 10 months. Tunnelling took place by means of drill+blast over the entire length in the average to large-grain granites of the Triberg Granite Pluton. The quartz content, which was mainly responsible for wear, amounted to between 40 and 50 %. ln the process, 1,315 m of the drive in the standard cross-section was undertaken in excavation class 2, which foresaw a 3 m length of advance and a reinforced 10 cm thick crown excavation. Following a short tunnelling phase, the prescribed crown excavation was changed to a full-excavation. Rates of advance of up to 12 m/d were attained during full-excavation. As forecast, there were only restricted amounts of ingressing water. The maximum inflow amounted to 0.3 l/s. After the driving operations were concluded, waterproofing was carried out. The umbrella seal was produced using a 500 g/m² protective fabric and a 2 mm thick FPO membrane. DIN 200 pipes made of PVC-U were installed for draining the underground water at the sides. Once the sealing Operations were in progress, the verges and vaults were concreted on the rise from north to south. The standard block length for the permanent lining amounts to 10 m. Curing was undertaken by 3 back-ups. The formwork carriage was devised in such a way that it could be used in sectors with or without the intermediate ceiling. The lay-bys were shuttered using a steel frame formwork system with timber sheathing. An out of the ordinary documentation of the construction process pertaining to the complete project was compiled by the "Web-Wühlmäuse" from the Triberg secondary school and made available on the Internet. The documentation describes all major events backed by illustrations and must be commended for the high quality of the articles. Interested parties can find the Web page under: www.tunnel-hornberg.de.

 

  • Country: Germany
  • Region: Baden-Württemberg
  • Tunnel utilization: Traffic
  • Type of utilization: Road tunnel
  • Client: Federal Republic of Germany, Land of Baden-Württemberg
  • Consulting Engineer: Bung Beratende Ingenieure, Ing.-Büro Bernd Gebauer (execution)
  • Construction monitoring: Bung Beratende Ingenieure
  • Contractor: Strabag AG, Herrmann Kirchner Bauunternehmung GmbH
  • Main construction method: Trenchless
  • Type of excavation: Drill-and-blast
  • Lining: Shotcrete
  • No. of tubes: 1
  • Tunnel total length: 1,884 m, 1,804 m of which driven by trenchless means
  • Cross-section: 83.2 m² standard cross-section with intermediate ceiling; 80.6 m² without intermediate ceiling; 139.4 m² (lay-bys)
  • Contract Volume: € 24 million
  • Construction start/end: April 2002 to July 2005
  • Opening: July 2006