Schmücke Tunnel - BAB A71

As part of the building of the new A 71 between Sangerhausen and Erfurt the ecologically invaluable Schmücke heights have been crossed by a roughly 1,725 m long twin-bore tunnel. The two tunnel tubes with a RQ 26 T cross-section and set some 22 m apart were excavated by mining means using the NATM over a distance of about 1,660 m. The tubes are linked every 300 m by cross passages. The minimum overburden amounts to about 16 m in the vicinity of the Weingartental valley with the maximum overburden some 62 m. Running from north to south lower, middle and upper coloured sandstone, lower, middle and upper shelllime and lower keuper layers have to be negotiated. On account of its evolution process the rock in the Schmücke area is deconsolidated as a result of pronounced fault zones running from NW to SE. Furthermore different dimensioning water levels must be taken into account, which rise from between 10 m above the roof in the middle coloured sandstone and approx. 16 m in the upper coloured sandstone (Weingartental) right up to 30 m in the middle shell lime. On account of the relatively low permeabilities lengthy periods were expected to be required for the rock to drain. As a consequence 35 deep wells in 3 rows were set up in advance of the excavation (to the right and left of the tunnel as well as in between) at depths ranging from 35 to 85 m, which operated to provide a combination of vacuum and gravity drainage. ln this way up to roughly 85 m³ of water was removed per hour and after only 2½ months the groundwater level in the northern section had been lowered beneath the tunnel floor so that the rock was more or less dry in time for the drive. The two directionally separated tunnel tubes were excavated parallel to one another with a counter-drive. Depending on the geology that was encountered the drive was mainly performed by drill+blast although an excavator was applied in some sections. Owing to the continuing presence of division planes and the in part pronounced deconsolidation of the rock a high degree of supporting was needed with continuous securing of the roof using lances. However, there was largely no need for two-layer pipe umbrellas, which had originally been projected. It was possible to excavate both tunnel tubes with this method within a year. On account of its location in the groundwater the tunnel inner shell was produced as a pressure water proof structure with an outer plastic sealing membrane. Once the 45 to 60 cm thick waterproof reinforced concrete inner shell was produced to be secure against uplift, the drainage system was deactivated. The original underground water level had been restored in the interim. After filling the base invert the cable pipe columns, the extinguishing water line and the drainage lines were laid. Emergency footpaths and a concrete carriageway were produced during the final working phase. For the first time in Germany LED technology was used for the lighting system applied throughout the Schmücke Tunnel.

Country: Germany
Region: Thuringia
Tunnel utilization: Traffic
Type of utilization: Road Tunnel
Client: Federal Republic of Germany, Thuringia
Project Engineer: DEGES, Deutsche Einheit Fernstraßenplanungs- und -bau GmbH
Consulting Engineer: Müller+Hereth Ingenieurbüro für Tunnel- und Felsbau GmbH
Contractor: Baresel AG/Alfred Kunz/Hermann Kirchner
Main construction method: Trenchless
Type of excavation: Drill-and-blast/Excavator
Lining: Shotcrete
No. of tubes: 2
Tunnel total length: 1,720 m (east tube), 1,729 m (west tube)
Cross-section: 109 to 147 m²
Contract Volume: approx. 72 mill. Euro (roughwork)
Construction start/end: 40 months?
Opening: 2008