Brixlegg Tunnel, Lower Inn Route

The twin-track Brixlegg railway tunnel was produced by the NATM with an excavated cross-section of 110 to 130 m² and a total length of 4,195 m as part of the Brenner access routes. In this connection 723 m of the main tunnel and roughly 2,250 m of the 2,500 m long rescue tunnel were built when driving the Brixlegg East exploratory heading. Cross-passages link the main tunnel with the rescue tunnel at 500 m gaps. The second access heading "Brixlegg Middle" possesses a length of 330 m. The excavation was undertaken entirely by drill+blast. In the west the contract section ended as a "stub" tunnel. In the east access was possible via a 150 m long sheet pile excavation pit, protected by a thin cut-off wall enclosure. The mined east portal of the tunnel is located in the southern hard rock flank of the Inn Valley. From that point the drive underpassed the Alpbachtal valley to the south of the centre of Brixlegg. Towards the west the route runs just to the south of the former "Mühlbichl" mining district, crosses the "Matzenpark" valley filled with soft material and leads over a ridge of hard rock and the former "Matzenköpfl" mining district back to the Inn Valley floor. The hard rock found on the southern fringe of the Inn Valley consists of series of sediments from Triassic Alpine limestone. There are also deeper, older and metamorphic sections of decomposed rock such as black dolomite and "Wildschönauer" slate. On account of the Alpine tectonics there is a complex rock structure including the Hauskogel and Hohenegg nappe systems. The area's hydrology is characterised by alternating water-bearing and impermeable layers with steep deposits of strata resulting in the formation of a cavity system. By lowering the groundwater protected by a cut-off wall until the inner shell was installed there was no trouble at all even in penetrating the pronouncedly water-bearing zones. Along roughly 75% of the tunnel a reinforced inner shell with an all-round seal (3 mm PVC membrane) was produced, which was designed to cope with up to 6 bar of water pressure. The remaining part of the inner shell was completed using an umbrella drainage. The roughwork operations were accomplished in only 24 months when the final inner shell vault was concreted. The existing rescue tunnel was used to allow work to forge ahead at up to four points of attack simultaneously. Double sets of formwork were installed to speed up the concreting work.

• Country: Austria
• Region: Brixlegg
• Tunnel utilization: Traffic
• Type of utilization: Railway Tunnel
• Client: Brenner Eisenbahn Gesellschaft {BEG}
• Contractor: Bilfinger Berger AG
• Main construction method: Trenchless
• Type of excavation: Drill-and-blast
• Lining: Shotcrete
• No. of tubes: 1
• Tunnel total length: 4195 m
• Contract Volume: 93 mill. Euro
• Construction start/end: 2004 till 2006