When mining engineering protects everyday mobility
Diagram of the installation of a jet grouting column.
© Eiffage Fondation
A large-scale operation applauded by regional stakeholders
At the end of July 2025, the backfill of the former Machine Anglaise mine shaft subsided, under the right-hand lane of an interchange on the RN488 at Saint-Etienne. This is a major artery that carries up to 2,200 vehicles an hour at peak times, and is bordered by a high-speed fibre-optic network. GEODERIS quickly determined that the mine was the cause and had the right lane blocked off and the speed limit of the left lane lowered.
In coordination with the DREAL, GEODERIS and the Direction Interdépartementale des Routes Centre-Est (DIRCE), and with the support of several companies including Antea Group (the prime contractor), Eiffage, SIC INFRA 42 and SDRTP, BRGM mobilised its teams to make the roadway safe and enable it to be reopened.
After an emergency geotechnical survey and study phase, jet grouting was chosen as the best consolidation method. This technique involves constructing intersecting vertical columns of cement-grouting to form a stable plug of the shaft. This meant that the work could be carried out in a relatively short space of time, while keeping the left-hand lane open to traffic and preserving the utility networks close to the collapsed area.
The operation was carried out smoothly and on schedule and is a perfect illustration of the technical expertise and cooperation between all the players involved in public safety.
