RD1091 diversion at “Séchilienne Ruins” – Isère, France

The RD1091 road diversion project at the well-known “Séchilienne Ruins” place consists in shifting the alignment of the road to the opposite hillside in order to protect it from a predicted 3 million m3 landslide (this scenario is assumed to be the most probable in the short and medium terms by the experts).

This deviation, about 1000 m long and costing a total of €30M, includes a large excavation in the Montfalcon micaschists: maximum height 40 m with an excavated volume of 200,000 m3 and an exposed surface of 15,000 m².

The height of the cutting and the poor quality of the soil mass (micaschists globally highly fractured, presence of bands of coal-bearing formations and high water circulation) require reinforcement by dense soil nailing: more than 45 km of nails combined with shotcrete facing on 4/5ths of the surface.  

TERRASOL was involved in the main phases of the project as geotechnical assistant to the Project Manager (Conseil Général de l’Isère): design and tender documents in collaboration with SITE ETUDES, VISA approval of the detailed design, and geotechnical follow-up of the works started in spring 2013 and carried out by the GUINTOLI/Bianco/NGE/GTS consortium.

Terrasol’s achievements:

  • Design and tender documents
  • Control of detailed design
  • Geotechnical follow-up of works
PERIOD :  2012 - 2013
Owner : Conseil Général de l'Isère
Project Manager : CG38
Main contractor : GUINTOLI / Bianco / NGE / GTS
Main specifications :  

  • Diversion of 1 km
  • Excavation of 200 000 m3 (until 40 m high)
  • 45 km of concrete nails