The Tunnel du Chambon: POWER SET Bolts stabilize important Connection between Grenoble and Briançon

The Tunnel du Chambon in France, which was opened in 1935, is an important connection between Grenoble and Briançon. The tunnel forms part of the Route Départementale 1091 and is located above Lake Chambon. In the spring of 2015, a landslide was detected in this area that had caused cracks in the tunnel lining and invert despite its having moved only a few centimeters per year. On April 10th 2015, the tunnel had to be closed as a consequence of the damage caused by the rock movements.

As the population of the Haute-Romanche Valley was completely cut off by this closure, an emergency route was built on the opposite lake shore that was opened in November 2015. However, this road is only able to accommodate approximately 700 vehicles per day. A long-term solution was urgently required to prevent further damage to the region’s economy as a result of the tunnel closure.

Stabilization of the areas in question was not economically and technically feasible so that the decision was made to build a new tunnel structure that will make a wide-ranging, 500m long detour around the landslide. The new bypass tunnel will be excavated from the inside of the existing tunnel and will then open out into a smaller, existing tunnel. In total, the Tunnel du Chambon will be lengthened by 240m, so that it will have a total length of 990m.

To stabilize advancement, DSI France produced and supplied Type PS 50, 300kN, 4m long POWER SET Self-Drilling Friction Bolts including 200/200/12 anchor plates. The patented POWER SET One-Step Bolt System ensures a safe and easy installation as well as immediate load-bearing capacity. Furthermore, the system is characterized by its high flexibility in regard to changing rock conditions.