Tranche 360 "Sedrun Tunnel" involved the creation of the two main tunnels of approx. 6,300 m each, and the multi-function station caverns. Access to the underground construction site was only possible through two vertical shafts of approx. 800 m depth, and of 7 m and 9 m in diameter respectively.
The tunnelling was carried out simultaneously both north and south from the cave constructed at the foot of the shaft.
The excavation was carried out both with explosives and by mechanical means. The excavation sections were between 60 and 134 m², reaching up to 220 m² in the caves.
The rock was favourable in part, but we were also faced with high rock pressures that made it necessary to use sliding ribs to reduce distortions.
The safety measures in the construction phase consisted of anchors, forepoling and shotcrete. The final lining of the arch and invert differed according to the geo-mechanical conditions encountered.