Extracted, sorted, reused: a virtuous cycle for building materials

In France, legal developments have made it possible to recover and reuse construction site soil that was previously considered waste. Sorting, treating and reusing soil and excavated material not only saves raw materials but also reduces the related transport and costs. With a view to making the best and safest use of these natural resources, BG has helped map plots of land in the Île-de-France and Normandy regions, with a view to moving from demolition and disposal to recovery and reuse.

The reuse of natural resources on construction sites is at a turning point. Mineral materials extracted from excavations and tunnelling and soil from brownfield sites, for example, are no longer considered as waste, but increasingly as raw materials. This paradigm shift has advantages in terms of both ecology and performance.

Imagining alternatives to final disposal of excavated soil

Nathalie Monin, Head of the Large Scale Projects France unit within BG’s Infrastructure and Transport Sector, emphasises the proactive approach of the group’s engineers: “Categorising materials, whether from demolition or excavation sites, helps define their possible uses, in order to give them a second life. Our engineers are working with users (storage facility managers, quarrymen, cement manufacturers, etc.) to find solutions, and with government departments to advise on the necessary regulatory changes.”

Environmental legislation now requires better management of natural resources on construction sites, but the BG group didn’t wait for this development to offer its skills in managing excavated material. It has been collaborating on complex projects, such as the urban development of Île de Nantes, with its rich industrial past, and advising and proposing solutions for the tens of millions of cubic metres of excavated material that will be generated by major infrastructure projects such as the Lyon-Turin railway or the Grand Paris Express. With recognised expertise in this field, BG recently helped develop a soil map for the Île-de-France and Normandy regions as part of the GeoBaPa project.

The geochemical level of these soils was evaluated in order to anticipate their reuse by determining how to align or make the excavated material chemically compatible with the sites that can receive it.

Rebuilding safely

Soil traceability is a major issue in the management and use of excavated soil. For Benoît Maréchal, Head of BG’s Environment and Polluted Sites unit, this parameter guarantees “the optimal and safe use of soil”. In the context of site redevelopment, when it comes to rebuilding without endangering the population, many technical options are available for reusing extracted soil. If the land is polluted, the material can be subjected to the appropriate intensive treatment and used off-site as fill, for example. “Such off-site use is highly regulated, particularly in France. It requires a very specific methodology. We must be able to specify where the soil comes from, its composition, what treatment it has undergone and what use is made of it.” The other approach consists of using the soil onsite, often as sub-layers, after screening to separate different sized soil fractions (sand, gravel, etc.).

Reusing some of this natural resource means less of it is disposed of in landfills, which also reduces the transport of materials. In the past, it cost less to produce and transport materials than it did to treat and manage them. “There has been a trend reversal, with the implementation of sufficiently optimised materials management models that make it possible to find outlets for excavated soil and organise logistical loops,” observes Benoît Maréchal. For this doctor of geology, given the “significant potential of excavated soil, we have an obligation to develop its use.”

(Article taken from BG Magazine 2022, updated version on the site)

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