Life cycle analysis
An eco-design tool
Life Cycle Assessment (LCA) can be used as a decision-making and eco-design tool.
The ISO 14006 standard defines eco-design as ‘a systematic approach that takes into account the environmental aspects of the design and development process with the aim of reducing negative environmental impacts throughout a product’s life cycle’.
Eco-design is at the very heart of the ecological transition in underground structures. It reduces environmental impacts (particularly carbon footprint, consumption of natural and energy resources, etc.) throughout the entire life cycle: from design to construction and operation, through to eventual end of life. Innovation and digital transition support and promote eco-design.
Life Cycle Assessment (LCA) is a multi-stage, multi-criteria method for quantifying the environmental impacts of a structure throughout its entire life cycle. It is based on the ISO 14040 and 14044 environmental management standards.
The objectives of life cycle assessment (LCA)
A LCA approach applied to underground structures makes it possible to:
- determine their environmental impacts,
- identify the stages of the life cycle or aspects that can be improved,
- compare innovative solutions and variants that meet the defined objectives.
LCA can also be applied to a more limited scope, such as a construction solution or a material.
LCA of underground structures provides objective analysis elements for the decision-making process, the challenge being to better support underground construction projects and better understand the areas with the most significant impact, in order to prioritise the efforts to be made. LCA can also be useful for defining contract award criteria. A bonus/penalty system can then be put in place to verify that objectives have been achieved and commitments have been met.
When and how should life cycle assessment be used?
There are three possible uses for LCA, depending on the stage of the project:
- At the opportunity study stage: the most relevant scale of consideration is that of the infrastructure, comparing different route options;
- At the design and then execution study stage: the scale of consideration is then that of the tunnel;
- The ‘construction’ stage (record of works executed); the scale of analysis is that of the tunnel.
The first two stages relate to eco-design, as defined above. Solutions or scenarios are compared within more or less restricted scopes (e.g. comparison of low-carbon segments and ‘conventional’ segments) with assumptions made for the choice of data that are not yet known at these stages of the project.
The third possible use of LCA is to carry out an environmental assessment. This no longer involves comparing scenarios or solutions, but rather evaluating in detail the environmental impacts of the tunnel in order to ensure that the client or contractors’ environmental commitments are being met.
The stages of life cycle analysis
The overall life cycle analysis approach covers the entire life of the structure, breaking down its life cycle into five main stages:
- manufacture of materials,
- transport,
- construction of the structure,
- life of the structure,
- end of life.
Example of elements included in the life cycle analysis of an underground structure
The various items that can be included in the scope of a tunnel’s LCA are presented in the diagram below.
Feedback
Thanks to the results of studies conducted by the CETU, we now have an idea of the scale of the climate change impacts of structural elements of an underground structure, in the case of conventional excavation. The case of tunnel boring machine excavation is currently being studied.
The orders of magnitude obtained for lighting (excluding LEDs at the current time) and ventilation equipment are 5 to 10 times lower than those for structural elements. Ultimately, LCA will make it possible to cover the entire life cycle of a tunnel with all its subsystems.
CETU’s research activities
The CETU co-supervised a thesis on ‘Assessing the environmental impacts of TBM excavation of underground structures using Life Cycle Assessment (LCA)’. This research was conducted in collaboration with the Navier Laboratory (Ecole des Ponts, CNRS and Gustave Eiffel University), in partnership with the Lyon-Turin Euralpin Tunnel (TELT) and Herrenknecht.
CETU is also involved in the ‘S-Pass’ project. A thesis is planned in collaboration with the Navier Laboratory at ENPC. Its objective is to evaluate the contribution of underground structures to sustainable cities.
In addition, the CETU has been involved in the French Civil Engineering Association’s Ecodesign working group and will continue this work within the framework of the DIOGEN group (Civil Engineering Impact Data).
Publications
AFTES recommendations
Within the scope of the French Association for Tunnels and Underground Space (AFTES), the CETU chairs AFTES WG41 ‘Underground works and sustainable development’ and, in this context, is currently preparing a recommendation on Life Cycle Analysis applied to tunnels (publication planned for 2025).
Conference articles
‘Ecological transition in tunnels’: L. D’ALOIA SCHWARTZENTRUBER, C. LARIVE, L. BAUCAL-POYAC, (CETU), AFTES International Conference 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 (Ecole des Mines Saint Etienne), AFTES International Congress 2023
‘Initial approach to assessing the environmental impacts of tunnel boring machine excavation through life cycle assessment (LCA),’ L. BAUCAL—POYAC, L. D’ALOIA SCHWARTZENTRUBER (CETU), B. AMOR, LIRIDE, Canada, A. FERAILLE, (Laboratoire Navier: Ecole des Ponts Paristech, UGE and CNRS), AFTES International Congress 2023
Publications in scientific or professional journals
‘Environmental assessment of the Siaix tunnel safety gallery’, L. D’ALOIA-SCHWARTZENTRUBER, C. CABUT (CETU), M. MASSONNAT (DIR Centre-Est), G. LEYMARY (EVEA-Conseil), AFGC Civil Engineering Days, June 2021
‘Life cycle analysis of lighting and ventilation in road tunnels,’ E. CHARLES, M. YAGHZAR, L. D’ALOIA-SCHWARTZENTRUBER (CETU), Tunnels et Espaces Souterrains No. 278, 2021
‘Life Cycle Assessment (LCA) applied to underground structures,’ L. D’ALOIA-SCHWARTZENTRUBER, Academic Journal of Civil Engineering, volume 40, 2022
‘Life Cycle Assessment (LCA) applied to the excavation of underground structures’, L. BAUCAL-POYAC, L. D’ALOIA SCHWARTZENTRUBER (CETU), A. FERAILLE (ENPC), Academic Journal of Civil Engineering, volume 41, 2023
‘Underground structures from an environmental and climate perspective’, L. D’ALOIA-SCHWARTZENTRUBER, J. BURDIN (Consulting Engineer), Mines et carrières no. 314, June 2023.
‘The eco-design of civil engineering structures: a paradigm shift,’ B. DAUBILLY (Cimbéton), P. CATHELAIN, J. ARMENGAUD (NGE), P. BISCHOFF, J.B. SIMON (Eiffage Infrastructures), S. BRAYMAND (University of Strasbourg), L. D’ALOIA-SCHWARTZENTRUBER (CETU), M. ROYER-MULLER (Construiracier), J.C. SOUCHE (IMT Mines Alès), S. BETHMONT (SETEC TPI), Revue des routes et de l’aménagement, No. 1003, April 2024..