Utilization of industrial by-products - Coal shales: site of Dourges

Coal shale is a by-product of the hard coal mining industry. With the aim of conserving conventional mineral resources, the slag heaps of the Nord-Pas-de-Calais region represent an important source of alternative materials for public works. However, with red shales and the hardest shales becoming increasingly scarce, the use of softer, conventional shales requires prior treatment with road binder before they can be used as base courses for heavily trafficked roadways. Prior to the construction of the Dourges multimodal platform, no large-scale use of this type had been undertaken.

For the general earthworks of the "Delta ³ " multimodal platform in Dourges (Pas-de-Calais), in service since December 2003, the client, the project manager and the contractor worked closely together to optimize the reuse of coal shale from the slag heap around which the structure is built. Given the evolving nature of the slag heap, the company carried out an in-depth study into the reclamation of coal shale by treatment with road binder, developed an original treatment procedure, and carried out the worksite by treating a large quantity (around 620,000 m ³ ) of shale, in order to create backfill for wetlands, earthworks, road and rail sub-bases, as well as certain rail sub-bases.

At the Dourges site, the reuse of shale for backfill and road and railbed sub-base optimized the thickness of pavement structures and enabled the project to be completed to the highest standards of quality, on time and cost-effectively.

At regional level, the reuse of shale from the Dourges slag heap has generated a saving of 5 million tonnes of quarry materials, while preserving the environment. This full-scale experiment could be repeated for road projects in the Nord-Pas-de-Calais region.