Issue link: http://read.dmtmag.com/i/653001
I DA U N I V E R S A L M a rc h -A p r i l 2 0 1 6 21 Diffi cult karstic limestone and squeezing conditions are being tackled for the fi rst ascending tunnel – the Bossler. Part of this tunnel is driven by an 11.3m Herrenknecht TBM, while the remainder is drill and blast methods. e same Porr-led joint venture is performing this work. Porr has also just completed the 4.8km long Steinbühl tunnel, which continues the upward climb a er a 485m bridge over a narrow valley. Despite further diffi cult karstic limestone sections, this twin bore has gone well, and breakthrough was expected to be celebrated on November 6, six months ahead of schedule. A further so ground tunnel of 7km is still in prepa- ration along the line. Even bigger high-speed tunnels are underway through the Alps, linking northern Europe to Italy. e largest is the world record 57km-long Gotthard Base tunnel, up to 2,500m deep, where track laying is complete and the opening is expected to be in June next year. e AlpTransit scheme includes a second tunnel further south, the 15.4km long twin-bore Ceneri where drill and blast operations with Sandvik rigs and a Rowa backup system are nearly complete. is was one of the fi rst major projects for Agir conveyors. Two southern drives were completed in March, and more diffi cult 8km northern drives will fi nish by the end of the year when rail and signaling work begins. e Ceneri will shave an additional 10 minutes from the Zurich to Milan route when complete. Austria to Italy Meanwhile, attention has moved to Austria and Italy, where not only the great Brenner Pass base tunnel is well underway, but two more base tunnels as well – Koralm and Semmering. e Brenner, from Tyrolean capital Innsbruck to Fortezza in Italy, forms part of the Trans-European Network (TEN-T) route from Berlin to Palermo. It is comparable to Gotthard at 55km long and has a maximum cover of 1,800m. If taken together with a 9km linked bypass tunnel at Innsbruck for trains heading onwards, it will claim a world record length of 64km. Between two single- track main bores of 8.1m in diameter is a smaller central service tunnel of just under 5m inner diameter and running 12m lower. It serves for later maintenance and drainage, but is also vital for exploration and geological investigation, according to the client, the Austro-Italian Brenner Base Tunnel Company. Preparation for the main tunnel drives has been underway for several years, with fi ve major access adits virtually complete, including a 6km length of the explor- atory tunnel from Innsbruck. e most important work recently has been a 1.5km- long, conventionally excavated section across the Periadriatic fault on the Italian side. is tectonically crumbled rock was potentially a major obstacle, but while the fractured rock was diffi cult going, it has proved passable. e same contract, completed this year, also excavated and lined the fi rst two 1.5km sections of the main bores. e next major work is an additional 15km of explor- atory tunnel being made with a Herrenknecht gripper TBM southwards from the initial Innsbruck section. It started in October a er assembly in an underground cavern. e €380 million multipart contract was let to Austrian contractor Strabag with Salini Impregilo from Italy in September last year. Work also includes completing more access points in the Innsbruck area, and a long 9km drill and blast drive parallel to the bypass tunnel as a safety tunnel. Austria has another trans-European high speed link underway, upgrading the line from Vienna to Graz, and with an entire new line section onwards to Klagenfurt. A key feature of the link is the 32.8km Koralm tunnel with maximum cover of 1,200m, and like other base tunnels, it has a very fl at gradient. Apart from a small 1.5km portal section begun in Story continued on page 22