Supporting the transition to a circular economy
Underground structures can contribute to the transition to a circular economy, in particular by:
- optimising the use of natural resources (economising on the choice of materials and equipment),
- reusing and recovering excavated materials through better management,
- recycling and extending the service life of equipment.
These principles are an integral part of the eco-design of structures (lien vers la rubrique life cycle analysis).
Through its research and engineering work, the CETU aims to develop solutions and provide economic, technical and methodological input to support professionals in making and implementing sound choices. This support must also be provided by monitoring changes in regulations and assessing their implications for the profession.
Optimising the use of natural resources
First and foremost, this involves optimising the design of the structure, both in terms of structural elements and equipment. This optimisation is accompanied by an informed choice of construction materials and equipment. Tunnels and underground structures cannot be designed without considering the characteristics of the materials and the interactions between the structural elements and the choice of equipment (e.g. the impact of the design of tunnel walls on lighting systems).
Optimising a tunnel’s design can therefore result in savings in materials and a reduction in the amount of equipment required.
It is also possible to save natural resources by promoting the use of materials from recycling channels or by choosing equipment that is ‘more’ recyclable. Tunnel construction requires large quantities of materials that often have a very high carbon footprint, such as concrete and steel. However, innovations in materials and construction methods can improve this carbon footprint: the use of low-carbon, very low-carbon or even ultra-low-carbon concrete, or the choice of recycled steel, etc. One example is the ultra-low-carbon tunnel segments tested on certain lines of the Grand Paris Express project.
Some equipment can also be reconditioned or retrofitted.
Finally, a territorial approach to the choice of materials and equipment, as well as to waste disposal, can also lead to optimised use of natural resources within a given territory. For example, it is possible to take advantage of a suitable source of recycled materials close to the construction site, thereby limiting transport and thus the impact on the environment. Regional planning documents help to support such approaches.
Better management of excavated materials through reuse and recovery
The management of excavated materials during the construction of underground structures is a relatively recent issue that has gained momentum over the last ten years due to major construction sites and underground projects, both in France (TELT, Grand Paris Express, CERN’s Future Circular Collider, Cigéo, new railway lines and metros, etc.), or internationally.
The CETU supports project owners on this issue, which has become a major concern due to the questions it raises in terms of preservation of natural resources and environmental impacts. This issue must now be addressed within the scope of the transition to a circular economy. It requires not only consideration of the future of these materials, but also reflections on industrial and territorial ecology and the eco-design of underground structures, in terms of materials.
CETU research activities
Life cycle analysis of excavated materials
As part of a postdoctoral programme supervised by CETU and the École des Mines de Saint Etienne, a life cycle analysis methodology was applied to the assessment of the environmental impact of excavated material management scenarios. This work, supported by ADEME, was the subject of a case study on the extension of Lyon’s metro line B with the support of the local transport authority, SYTRAL.
Also as part of its life cycle analysis of excavated materials, the CETU is conducting a study on two specific indicators: ‘resource depletion’ and ‘changes in land use’.
This research will lead to the development of a methodological guide on the use of excavated materials, which in particular will address the impacts of excavation methods on excavated materials and their uses, as well as the production of aggregates on site.
The Future Circular Collider Innovation Study (FCCIS) project
At the European level, the CETU is heavily involved in the FCCIS (Future Circular Collider Innovation Study) project as the lead partner responsible for the deliverable that will form the basis of the excavated materials management plan for the Future Circular Collider. The CETU also supervised postdoctoral work on ‘Territorial analysis for the establishment of a recovery chain for excavated materials in underground works with an application to CERN’s Future Circular Collider project’. This work was carried out in collaboration with the École Normale Supérieure de Lyon.
Also as part of the FCCIS project, the CETU was a member of the jury for the ‘Mining the future’ call for innovations, which aimed to promote research and encourage the emergence and development of innovative uses for materials that are currently difficult to recycle, such as molasses. Molasses constitute the predominant material along the route of CERN’s future particle accelerator.
The REMATCH project
CETU is also involved in the Franco-German research project REMATCH, which uses artificial intelligence techniques to analyse images and data from tunnel boring machines in order to improve the recycling of excavated materials.
Implementation of the AGEC law
Beyond the issue of excavated material management, the CETU is working to implement the principles of the AGEC law of 10 February 2020 on the circular economy and the fight against waste. This law introduces the idea that a minimum percentage of reused or recycled materials must be incorporated into construction products. Although such incorporation rates are not (yet) mandatory in the civil engineering sector and therefore in underground structures, this aspect must also be taken into account in the context of the transition to a circular economy. In particular, the CETU monitors concrete specifications and regulatory developments that now incorporate low-carbon aspects.
CETU publications
In 2016, the CETU published a document on the topic of excavated material management (available in French). This document aims to assist project owners in implementing a management approach for excavated materials in underground works, from the design studies through to the construction phase. It addresses the following points:
- the specific characteristics of excavated materials depending on the geological nature of the terrain encountered and the excavation method used;
- scenarios for managing excavated materials, described and analysed in relation to the responsibilities of each of the parties involved and the administrative procedures;
- the main uses and channels depending on the nature of the excavated materials;
- the role of the parties involved throughout the projects (whether road or rail).
- The management of excavated materials and waste is also covered in the Tunnels Master Folder, Document No. 5: Environment, 2011.
Conference papers
“From the production of excavated materials to the preservation of mineral resources”,L. D’ALOIA SCHWARTZENTRUBER, D. CHAMOLEY, A. CHERREY, L. MONGEARD (CETU), GC’2021 Technical Days
“Which tests for a rapid geotechnical characterisation of excavated materials for use as concrete aggregates? Application to the Lyon-Turin base tunnel” A. CHERREY & D. CHAMOLEY (CETU), World Tunnel Congress 2023
“Life Cycle Assessment (LCA) applied to the management of excavated materials in underground works: Case study of the extension of metro line B to Saint-Genis-Laval Hôpital Lyon Sud” - J. RODRIGUES (dss+, Geneva), L. D’ALOIA SCHWARTZENTRUBER (CETU), G. DUFOUR (SYTRAL), N. GONDRAN (École des Mines de Saint Étienne), AFTES International Congress 2023
‘Traceability of excavated soil, recovery as waste and non-waste – Case study of major works’, A. CHERREY (CETU), AFTES International Congress 2023
‘Regulatory context for the reuse of excavated materials in concrete aggregates’, D. CHAMOLEY (CETU), J. BLACHE, M. DIERKENS (CEREMA), L. D’ALOIA, A. CHERREY (CETU), AFTES International Congress 2023
Publications in journals
‘Reuse and recovery of excavated materials: underground structures from an environmental and climate perspective’, L. D’ALOIA (CETU), J. BURDIN (Consulting Engineer), Mines et Carrières magazine no. 314, June 2023.
‘Law and status of excavated materials in France’, A. CHERREY, L. MONGEARD, L . D’ALOIA and F. ROBERT (CETU), Tunnels et Espace Souterrain magazine no. 276, 2021.
Publications produced with the contribution of CETU
- Recommendations of AFTES WG35 ‘Management and use of excavated materials’, 2019 (in French).
Other publications
Further useful information on these topics can be found on the website of the Ministry for Ecological Transition (in French):