References

The upgrading of the RN 125 main road between Saint-Béat and Arlos in the French Pyrenees will enable to bypass the village of Saint-Béat by means of a tunnel through the Cap de Mount mountain. The village is renowned for its quarrying of white marble, the formation constituting most of the massif through which the tunnel is built.

The Guintoli – Solétanche – Solétanche Bachy Tunnels – Pizzarotti consortium has contracted TERRASOL and BMCI (a subsidiary of SETEC TPI) for the geotechnical and civil engineering detailed design of the tunnel. The 1018-metre-long tunnel was excavated by the traditional method using explosives, with a support mainly comprising bolts and shotcrete.
Despite a geology favourable to tunnelling (Marmorean limestone and good-quality marble, with limited fracturing), the works gave rise to some surprises: karsts at the northern portal, and substantial water inflow on the southern face.

The main difficulty of the project, clearly identified by the first explorations, was the interception by the northern safety tunnel of a glacial furrow filled with alluvial materials. Analysis of additional explorations from the tunnel and from the surface resulted in the proposal to cross this geological irregularity by means of an arched support reinforced by forepoling. The excavation of the main tunnel was completed in December 2013.

Terrasol’s achievements: