Short Distances with DSI: Supply of Ground Support Products for the Granitztal Tunnel Chain in Austria
The 130km long Koralmbahn is currently the largest project for extending Austria’s railway network. The new section establishes a direct connection from Graz to Klagenfurt, reducing travelling times in this area from 3 hours to 1 hour.
After the Koralm Tunnel, the approximately 6.1km long Granitztal Tunnel Chain is the Koralmbahn’s second longest tunnel system. The tunnel chain is located in the 7.8km long section between St. Andrae and Aich that is being built by a Joint Venture consisting of Implenia and Hochtief Infrastructure. The tunnel chain consists of three sections – a tunnel in the Granitz Valley that is being built using the open cut method, and two bored tunnels. The Deutsch Grutschen Tunnel is 2,556m long and the Langer Berg Tunnel has a length of 2,929m. Both tunnels are being built with 2 single track tunnel tubes each and are connected via the 597m long enclosure in the Granitz Valley. Between the double tubes of both tunnels, crosscuts are being built approximately every 500m. The excavation of the two tunnels will create approximately 1.3 million m³ of excavation material, 800,000m³ of which will be re-used for building the tunnels. The geology near the Langer Berg Tunnel is characterized by tectonic fault zones and highly changing formations so that a flexible and adjustable construction method was required. The tender stipulated that the excavation had to be carried out in accordance with the New Austrian Tunneling Method (NATM) because the use of a Tunnel Boring Machine (TBM) would have involved unacceptable risks. The mountain ridge near the Deutsch Grutschen Tunnel consists of Neogene and unconsolidated Miocene sediments. According to a cost estimate, tunnel driving in this area was also more economical using the NATM in comparison to a TBM. DSI Underground Austria as a system supplier produced and supplied all of the ground support products that were required to stabilize advancement, including OMEGA-BOLT® Expandable Friction Bolts, SN Anchors, the DSI Hollow Bar System, AT – TubespileTM, Ø 38 x 4 mm tube spiles, and POWER SET Self-Drilling Vacuum Tube Spiles. In particular, the AT – Drainage System was predestined for deep reaching drainage in highly variable formations. The system consists of an inner steel tube which is wrapped with a PVC-drainage pipe. It can be employed temporarily as well as semi-permanently during drainage work parallel to tunnel advances. The AT – Drainage System is characterized by a rapid length adaptation achieved by piece-by-piece installation, with a simple lengthening of the drainage tubes also being possible in limited space at all times. Another important feature of the system is the high directional accuracy of the drainage drilling. DSI supplied the Type AT – 76-DR Drainage System, T32 x 3,000mm AT – Drilling Rods, R32 shanks and R32-T32 transition pieces. To provide immediate support in the open span area, DSI produced and supplied 3 bar, Types P50/20/30, P70/20/30, P95/25/30 as well as P130/25/30 Lattice Girders including welded-on nut pairs, 1m long spacers and tilting bases with 3 struts. Excavation at the northern portal near St. Andrae was begun on April 24th 2015, and the tunnel chain is scheduled for completion in 2020.