Boulogne-Billancourt - Rehabilitation of the Trapèze East ground
Cleaning up works on a part of a former automotive factory
Until 1992 Renault operated a car manufacturing plant in the commune of Boulogne Billancourt. After operations ceased Renault requested the company Antéa to carry out investigations on a 10m x 10m sampling grid representing, for the works zone, 830 probes, 3,100 samples and 101,700 parameters analysed. These surveys enabled the soil quality to be quantified. Operations on this site over almost 100 years had resulted in localised infiltration of hydrocarbons and volatile organic solvents into the subsoil. The work of cleaning up the Trapèze Est site was entrusted to Sol Environment in March 2007. The preparation works necessitated shoring up a site boundary located at the edge of a public highway using secant piles and the creation of watertight treatment cells (11,500m2). The polluted materials (concrete and unsaturated and saturated soil) were selectively extracted using mechanical apparatus, transferred to watertight treatment zones and treated on-site before backfilling.
Acceptance of excavation limits and of clean, treated materials was done by sampling soil, concrete and soil gas by surface area units of 25m2 of ground and volume units of 60m3 of dispersed materials. These checks represented around 2,500 samples and 101,500 parameters analysed. Pumping into the alluvial deposits of the Seine by the commune resulted in hydraulic containment under the site. The hydrocarbons that had infiltrated became trapped in the alluvial deposits when pumping stopped. The excavation works under the water table conducted in open excavation or inside sheet-pile sections required skimming of the hydrocarbons released by the excavation works. 250m3 of free hydrocarbons were collected in this way and disposed of either in a special industrial waste incinerator or via a cement works approved for energy recovery. The biological treatment carried out through activation of autochthonous fauna by introducing oxygen and nutrients enabled the hydrocarbons adsorbed or absorbed in the soil to be broken down. During the biological treatment, an increase of around 1 million CFAs (colony forming units) was observed inside the treatment windrows, associated with an increase in temperature of approximately 10°C. 47,500m3 of earth polluted by hydrocarbons was treated in compliance with the cleaning objectives determined in a detailed risk evaluation carried out by Antéa and fixed by Prefectoral Decree. The earth treated on site was recovered for use as backfill on the site. The earth polluted by volatile organic compounds (chlorinated solvents and naphthalene) was treated by on-site venting. 1,500m3 of earth polluted by chlorinated solvents was treated on site and recovered for use as backfill after characterisation in batches of 60m3.
The concrete on the site, blocks and buried blocks, were broken up using hydraulic rock breakers and crushed into 20/80mm using mobile crushers. Thus 4,300m3 of concrete was treated on site and recovered for use as backfill after characterisation in batches of 60m3. The works were subject to specific working procedures depending on the tasks to be accomplished and to regular monitoring, both internal and external, of health and safety conditions. The laboratory analysis results form a large database enabling precise traceability of the materials extracted, treated and used as backfill.
Soletanche Bachy, and its subsidiary Solenvironment, provide solutions for pollution issues, involving, for example: inertisation of waste, rehabilitation and treatment of polluted sites, cleaning of discharge to required environmental control levels, construction of waste storage facilities, protection of groundwater.
A retaining shell is a slim shell structure used during vertical excavations. Unlike retaining walls, the weight of a retaining shell has little effect on its capacity to balance the pressures.
Through his subsidiary Sol Environment, Soletanche Bachy provides solutions to various pollution problems: stabilisation of waste, rehabilitation and treatment of polluted sites, cleaning of discharge to required environmental control levels, construction of waste storage facilities, protection of the water table.
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