One of the machines – a double shield 10.65m-diameter giant named Virginia – bored and lined 860m in March 2021, thereby setting a new monthly record at the jobsite. Project owner Austrian-Italian BBT SE also confirmed that the average daily advance for March was 27.7m, with a daily best of 36.75m. By early April 2021, the two machines in the BBT main tunnels had already covered over half the total distance toward their lot boundary, excavated mainly in ‘stable geologies’.
Contracting joint venture BTC S c.a.r.l (Astaldi, Ghella, PAC and Cogeis) is excavating the main tubes as well exploratory tunnels (to be followed by service tunnels) 12m below the main excavation.
Running through the central eastern Alps, the BBT crosses a challenging geology of quartzphyllite, shist, gneiss and granite located in the collision zone of the European and African tectonic plates. For most of the alignment, the overburden varies between 1,000m and 1,500m. Rock mass permeability in some places may need to be reduced by extensive grouting; environmental rulings prohibit lowering of the water table.
When completed, the 64km-long BBT will be the world’s longest rail tunnel, running through the Alps from Innsbruck, Austria to Fortezza (South Tyrol) Italy. Spaced up to 70m apart, the twin, single-track tubes will be linked by cross passages every 333m. The tunnel route is blessed throughout with particularly low gradients.