On 06.06.2012 consortium Condotte Cossi completed TBM excavation of the emergency tube of the Grand St Bernard tunnel. The 5,760 m-long drive, lined with precast concrete segments, was completed in 18 months.

The first 5 km of the drive was in mainly gneiss, with high compressive strength and presence of quartz and other highly abrasive materials. This necessitated an extraordinary refurbishment of the wearable elements of the 4.30 m-diameter head of the double shield TBM. In the final stretch of tectonized graphitic schists with high squeezing values, special mortars were applied to allow deformation behind the precast segmental lining. At one stage, the TBM shield locked and had to be released by manual excavation of two lateral passages. For the final section, advance was in single shield mode. For more click here and it/91. Visit www.sitrasb.it, www.condotte.com and www.cossi.com. 24/12.