Leutenbach Tunnel-B 14, Winnenden Bypass

The town of Winnenden is being bypassed to the west by a new route as part of the development of the B 14. In this section the 1,080 m long Leutenbach Tunnel underpasses the floodplains of the Buchenbach, a railway embankment as well as the Hungerberg. A roughly 659 m long section was driven by mining means. To the west and east approx. 371 and 50 m cut-and-cover sect ions connect with it. The tunnel consists of 2 parallel running bares each with 2 vehicle lanes. The tubes are linked by a drivable cross-section as well as two accessible ones. At the floodplains of the Buchenbach the tunnel cross-section is located in solid layers of upper shell lime, which are karstified in their upper layers. Above there are quaternary soft rocks, in part possessing a soft to pappy consistency. At the Hungerberg the tunnel passes through Letten keuper layers, which consist of intermittent solid Dolomite rocks and friable to extremely friable silt stones. The mined section was driven by drill+blast. On account of neighbouring residential areas a non-electric ignition method was selected. By means of some 100 ignition time stages it was possible to ignite all boreholes with a time delay in order to minimise the effect of vibrations. For the excavation the entire cross-section was divided into part-excavations- crown, bench and floor. Supporting was executed using two layers of reinforced shotcrete and an anchoring system. At the Buchenbach floodplain s pipe umbrellas were employed throughout for advance supporting. This was needed on account of the karstification of the upper shell lime in conjunction with the narrow gap of 1 to 2 m between the roof and the quaternary covering layers in the form of soft to pappy fluvial deposits. In the Letten keuper layers advance supporting with lances sufficed. In the tunnel section with pipe umbrellas on average rates of advance of 2 to 2.2 m/day were attained in the crown and in those with lances from 3.5 to 4.0 m/day. On account of the relatively small gap between the two tunnel bares - amounting to some 2 m - the intention was to first of all drive one tube to its full length and install its inner shell. Afterwards the second tube was to be excavated. After the drive for the first tube indicated that a central pillar of solid rock was present, the client and the contractor decided in spring 2007 on a staggered excavation. As a result the second tube was bored before the inner shell was installed in the first one. By applying this approach delays in construction caused by producing the excavation pit for cut-and-cover amounting to around 8 months were almost completely compensated for. The production of the inner shell was concluded in July 2008. At present the final jobs are being taken care of parallel to installing the operating technology. The project is due to open in mid-2009.

Country: Germany
Region: Baden-Württemberg
Tunnel utilization: Traffic
Type of utilization: Road Tunnel
Client: Federal Republic of Germany represented by the Regierungspräsidium Stuttgart
Consulting Engineer: Prof. Dr.-Ing. W. Wittke Beratende Ingenieure für Grundbau und Felsbau GmbH (WBI), Aachen; Boll und Partner, Ingenieurgesellschaft, Stuttgart
Contractor: Hermann Kirchner Hoch- und Ingenieurbau GmbH, Bad Hersfeld
Main construction method: Open/Trenchless
Type of excavation: Excavator/Drill-and-blast/Cut-and-cover
Lining: Concrete formwork/Shotcrete
No. of tubes: 2
Tunnel total length: 1,080 m (totaI), 659 m (mining means), 421 m (cut-and-cover)
Cross-section: 103 m² (2 tubes in each case)
Contract Volume: 39 mill. Euro (roughwork), 6 mill. Euro (operating technology)
Construction start/end: 2006-2009 (3.5 years)
Opening: summer 2009