The project consisted in creating a property development in Montbonnot-Saint-Martin including four-storey apartment buildings with or without an underground level.
Located about ten kilometres East of Grenoble, the Grésivaudan valley is known for being a level 4 seismic area on a scale of 5. In that region, the geotechnical substratum is located between 20 and 30 m deep, under a deep layer of loose sediment. The combination of geotechnical and seismic contexts as well as the heavy loads generated by the infrastructures imposed the search for a suitable ground reinforcement solution.
Menard chose to reinforce the ground using bi-modulus columns. This process consists in installing an inclusion, the lower part of which is made of a concrete shaft (rigid inclusion or Controlled Modulus Column) topped on the first two metres with a ballast inclusion such as a stone column.
The advantage of this process is that it can be performed at great depths (up to 45 m deep) while benefiting from the advantages of rigid inclusions (with high work rates and high drilling capacities) as well as the advantages of stone columns in seismic areas. With this method, the foundation slabs could be cast directly on the inclusions without requiring the installation of a load distribution structure.
In this complex geotechnical and seismic context, this ground reinforcement solution allowed to meet the most recent seismic regulations and to offer a cost effective alternative to piling.