ABSTRACT

The Berg Bock Highway Tunnel represents the southernmost link of the "Thuringian tunnel chain" of the new freeway A71 located in the eastern part of Germany. It comprises two tubes each 2700 m in length. From north to south, it passes through the Suhl granite, the base sediments and the porphyrite of the New Red as well as the layers of the Middle Bunter. The two tunnel tubes were driven by the shotcrete method within appr. 10 months. With four tunnel faces, maximum performances totaling appr. 30 mid were attained. Additional, supplementary demands on the safety conception, resulting from the findings from and the analysis of fire accidents in tunnels in recent years, had to be fulfilled in the execution planning at short notice. The inner lining is largely constructed using non-reinforced concrete. Reinforcement is only installed in the portal zones, in tunnel sections in less stable rock and in areas with a special cross-section as for instance cross connections and niches.

STRUCTURE

In the course of the new freeway (Autobahn) A71 connecting Erfurt and Schweinfurt, the Berg Bock Freeway Tunnel located between the exit "Suhl North" and the intersection "Suhl" represents the southernmost link of the "Thuringian tunnel chain" (Kleffner 2000). Two tubes each 2700 m in length are constructed (Fig. I). Each tube comprises two lanes each 3.75 m wide and two emergency sidewalks. The excavated cross-section of the tunnel ranges between 80 and 120m2.

From north to south, the Berg Bock Freeway Tunnel passes through the Suhl Granite, the base sediments of the New Red, the porphyrite of the New Red and the layers of the Middle Bunter (Fig. 2).

SAFETY CONCEPTION

The safety conception is based on the Standards for the Equipment and the Operation of Road Tunnels

(Figure in full paper)

(RABT 1994). This standard is currently being revised on the basis of analyses of fire accidents in tunnels in recent years. Additional, supplementary demands on the safety conception (BMV 2001) had to be fulfilled at short notice in the execution planning for the Berg Bock Freeway Tunnel.

The safety conception comprises nine connection drifts between the tubes at a distance ≤300m (Fig. 3). The connection drifts are equipped with emergency call niches and fire protection locks.

Three breakdown bays are furthermore situated in each tunnel tube with at a distance ≤600m. Three connection drifts close to the breakdown bays are passable for rescue vehicles.

(Figure in full paper)

HEADING AND SUPPORT

Heading and support of the tunnel were carried out by the shotcrete method. With four headings, both tubes were driven starting from the portals (Erichsen & Bachsleitner 2001; Schmidtmann & Erichsen 2001).

Heading in granite gruss

In the area of the northern portal (Fig. 4), the granite is very strongly weathered and grussed. As a consequence of the extreme degree of weathering and the strong water inflow, the following protective tunneling measures were carried out:

  • preceding drainage borings

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