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The Project 

The creation of the A41 motorway section between Annecy and Geneva involved staggered carriageways on the sloped section below Cruseilles, requiring the construction of large retaining walls:

  • A cut wall, with a maximum height of 11 m, made of reinforced concrete ground beams on 1-4 levels combined with tension members anchored in the molasse stratum ,
  • A reinforced embankment below the motorway, with a maximum height of 11.5 m, strengthened at the base by a ground beam and tension members .
    These structures were completed by a drainage system consisting of trenches and subhorizontal drains.

To meet tight deadlines, the project was optimized with integrated design and concurrent engineering.

Given the complex geotechnical context and the risks involved, this organization was accompanied by careful monitoring of the slope and the structures under construction, inspired by the observational method.

In addition, the designer worked alongside the contractors in the implementation phase to enable a fast response to any hazards (particularly local till instability due to drilling).

Challenges

Project owner
ADELAC

Period
2006 – 2008

Key figures
Cut wall: length 370 m x 11 m maximum height
Embankment: length 270 m x 11.5 m maximum height
Drainage: 1,300 m of transverse trenches and 20-30 m subhorizontal drains

Challenge
The slope was composed of clay and sandy loam on a substratum of molasse.
The site featured erratic circulation, with widely varying piezometric levels in terms of time and space, with local artesianism.
Finally, a government-protected wetland area was located directly above the structures.
These elements, combined with the seismic risk of the area, were integrated into the design.

The Assignment

setec als provided integrated project management for the consortium in charge of building the A41:

  • Variation studies in addition to conceptual design
  • Preliminary design
  • Detailed design
  • Design verification
  • Works monitoring