Schwarzer Berg Tunnel (2nd Tube)
The BAB A70 Schweinfurt-Bamberg-Bayreuth provides the expansive west-east link between the A 7 near Würzburg, the A 73 near Samberg and the A 9 near Bayreuth, which has gained added significance since German reunification. The final, roughly 2 km long, one-way part-section of the A 70 between the junctions of Knetzgau and Eltmann represented a real bottleneck, which urgently had to be rectified. As a consequence, the single-bore Schwarzer Berg Tunnel, which was built in 1986 and was previously operated bi-directionally, was provided with a new southern tube. The 722 m long new southern tube runs parallel to the northern one at a centre distance of roughly 60 m and is connected with it by means of 3 cross-passages through which traffic can run. The maximum overburden amounts to 71 m. The standard cross-section is accounted for by 2 lanes with an overall width of 10 m between the verges and emergency footpaths at both sides each 1 m wide. The excavated cross-section amounts to 102 m² in the southern tube and 30 m² in the cross-passages. The southern tube is located in practically horizontally bedded Lehrberg and reed sandstone layers of gypsum keuper. Clay silt stones containing gypsum are to be found at the centre of the mountain ridge, with both leached out rock as well as rock containing gypsum being encountered. In the portal zones the overburden consisting of soft ground extends to the tunnel profile. The maximum water level is located up to 3 m above the roof with the groundwater classified as acting aggressively against concrete. The excavation was undertaken divided into crown, bench and floor. In the soft ground section the rock was solely removed by mechanised means using a tunnel excavator; in "better'' rock blasting was employed. The cross-passages were driven in conjunction with the crown with the bench and floor drive produced retrogressively. The short lengths produced in soft ground amounting to 0.8 to a maximum of 1 m were in each case secured by structural steel mats and shotcrete (2 layer), face support, SN rock bolts and lances. Subsequently, the lengths of advance could be increased and the support thickness reduced. The underground water is removed via an umbrella seal and the flushable underground drainage system. The floor of the permanent lining is reinforced throughout, the arch only in the tunnel entrance areas and where there are niches. The superstructure in the tunnel consists of a frost protection layer, a hydraulic binder and a concrete carriageway. The tunnel operating technology complies with the RABT 2003. After completion of the southern tube, the existing northern tube is to be upgraded in keeping with the RABT 2003 regulations.
- Country: Germany
- Region: Bavaria
- Tunnel utilization: Traffic
- Type of utilization: Road tunnel
- Client: Federal Republic of Germany, Free State of Bavaria
- Consulting Engineer: Autobahndirektion Nordbayern, Müller+ Hereth, Ingenieurbüro für Tunnel- und Felsbau GmbH
- Contractor: Walter Bau-AG associated with Dywidag
- Main construction method: Trenchless
- Type of excavation: Drill-and-blast
- Lining: Concrete formwork
- No. of tubes: 1
- Tunnel total length: 722 m
- Cross-section: 102 m² (main tunnel), 30 m² (cross-passages)
- Contract Volume: approx. € 13 million (roughwork)
- Construction start/end: September 2002 to June 2004
- Opening: November 2004