Bruck expressway S35 contract 22 - Tunnelling through serpentinite / Brucker Schnellstraße S35 Baulos 22 - Vortriebe im Serpentinit

The main part of the about 7 km long Brucker Expressway S35 contract BL 22 consists of the two-bore Kaltenbach (1,100 m) and Kirchdorf (2,700) tunnels. The special feature was the sections through serpentinite, which extends right across the southern section of the Kirchdorf tunnel. Tunnelling through this rock containing asbestos was a novelty for all parties involved, particularly considering that there was almost no experience available from tunnel sites where white asbestos had been encountered. The main emphasis during the work was to avoid dust in the tunnel. The specified measures were unsuitable for a low-dust drive, because the heaped material could only be wetted on the outside. Only a revised concept with the loose material being mixed during loading produced the desired results in reducing dust. In addition, the dust was cleaned out of the air in the tunnel after each blasting round by water mist produced by snow cannons. At the same time, the air was exchanged through positive pressure and supporting extract ventilation, with the extracted air being passed through special asbestos filters. A lock system at the portal also prevented the escape of asbestos fibres to the outside world. The vehicles in the tunnel were cleaned with a tyre-washing plant and a washing beam. Water-mist curtains at the portal formed the separation to the open air. All workers in the asbestos-contaminated "black area" were provided with one-use protection suits and dust masks, which they had to give up for disposal at the lock when leaving the tunnel. The experience gained should serve as the basis for similar projects in the future.