“Useful materials production could become a condition for justifying and authorising a major urban development project.”
By Laëtitia Mongeard, post-doctoral fellow at Ecole urbaine de Lyon (Université de Lyon)
Read the original text in French. Translation made with automatic translator Deepl.com and revised by Lucas Tiphine
The Great Paris Express, the future Lyon-Turin rail link, and the extension or creation of metro lines in major cities are all major tunnel projects that will continue for many years. Although these works are largely invisible because they are underground, their scale results in the production of millions of tonnes of excavated material.
“A volume equivalent to filling 9000 Olympic swimming pools. A weight equivalent to 4,500 Eiffel Towers. The Société du Grand Paris (SGP), owner of the Grand Paris Express (GPE), knows how to use symbols to quantify the earth excavated for the needs of the future supermetro.
Between now and the end of the project, nearly 45 million tonnes of excavated earth will be produced to build the tunnels, stations and other ancillary structures.” Le Parisien, 25 October 2019
These materials represent a very important part of territorial metabolisms — understood as all the energy and material flows due to the functioning of human societies on a territorial scale. Moreover, their circulation has many environmental impacts such as the consumption of space for their storage, the risk of pollution linked to their physico-chemical characteristics or the greenhouse gas emissions attributed to their transport. All these characteristics make it a privileged object for research, particularly in geography, in order to analyse the links between society and development.
Dealing with construction waste
European and French regulations have been dealing with the subject of excavated material since the early 2000s, gradually imposing and specifying the obligation to manage ‘construction waste’ in line with the objective of a circular economy. The aim of these regulations is to control the environmental risks inherent in their circulation, particularly illegal dumping. The status of waste is accompanied by obligations in terms of traceability, treatment and outlets authorised to receive the materials. Hazardous waste must be handled by specific treatment or storage centres; non-inert and non-hazardous inert waste must be sent to recovery channels or to storage centres that are also adapted to their physical and chemical nature.
The regulatory injunctions relate in particular to reuse, recycling and other recovery practices, up to 70% according to the objectives set by the Framework Directive n° 2008/98/CE of 19/11/08 on waste. In 2019, the Auvergne-Rhône-Alpes region had a performance rate of 88% (rate of recoverable materials actually recovered). However, behind this very high recovery rate is in fact mainly the use of inert waste as quarry backfill, i.e. a reuse with little value in terms of the circular economy: the materials are simply put in place in the void left by the extraction, they do not replace natural materials in a construction process.
Although this use contributes to the restoration of sites, to their renaturation, it highlights the limit of circularity and with it that of the term “waste” which refers to a linear conception of development processes. These processes involve major projects whose implementation incidentally produces excreta, just as the industrial process produces waste, which must then be managed. Aware of the impact of human activities on the environment, is this end-of-pipe conception still adapted to the challenges of global change?
The usefulness of “waste” status to regulate practices
Construction professionals frequently mention the limits of “waste” status , which restricts the way in which materials can be reused and gives them a negative image. However, this status is not intended to reduce the intrinsic value of materials, but only to regulate their management, particularly through the traceability obligation. The “waste” status is not opposed to the already long-standing practices of companies concerned with integrating materials management into the creation of value within the operation. The 19th century demolisher was simply the mason of the future building site who recovered materials to be used; the 21st century demolisher often implements deconstruction practices that allow waste to be sorted, to pay the high price of storage only for non-valuable fractions and to reuse or even sell good quality materials.
Thus, on any construction site, many logics are at work to create material value, from the way operations are conducted to waste outlets choice. Law evolution leads professionals to take into account the value of the building sites materials in their practices. The 10th of February 2020 law on fight against waste and promotion of the circular economy presents an important evolution in this sense by transforming the “waste diagnoses” prior to demolition and rehabilitation sites — implemented since 2012 — into “product, material and waste diagnoses”. Behind the semantic evolution appears the will to apprehend the materials of building site as resources.
Is it possible to further reduce the impact of the construction site by taking waste into account at an earlier stage?
Can this regulatory evolution lead to a significant reduction of building site impacts? It is possible to carry out the reflection by considering the exceptional case of great development projects building sites and among them more specifically tunnels.
These projects scale means that very large quantities of materials are put into circulation, often over a long period of time, ranging from several months to several years. The extension of two stations on Lyon’s metro B alone requires a year’s worth of tunnelling; the Grand Paris Express project is set to last a decade. On an annual average basis, the quantities produced by the projects considered here alone represent 5 to 6% of the annual production of construction waste (reference year at national level in 2012).
The quantities of excavated materials involved require very early and specific waste management thinking, and call for the implementation of exceptional measures. Managing millions of tonnes of excavated material at a regular and intense rate requires the evacuation of the material from the construction site; this may involve the installation of a conveyor on the construction site and then evacuation by rail or by road, with numerous specific measures each time.
Unlike materials produced by demolition or earthmoving sites in urban areas, materials excavated in underground works are geological materials, sometimes equivalent to materials voluntarily taken from a quarry or mine. Moreover, they are not very polluted because they are extracted at depth. However, they are subject to varied geologies, possibly complex or still little known: when quarrying is carried out in an area chosen for the quality and homogeneity of the materials, the tunnel construction site is delimited by the desired location of the project and must deal with the geologies encountered.
For this reason and because they are excavated in the context of a development site, the materials, although geological and natural, will flirt with the status of waste depending on the possibilities of reuse on site, and part of the site will be devoted to the creation or preservation of their use value. This value depends on the sorting carried out among the excavated geologies and on the treatment of these materials, which are also impacted by the excavation techniques used (presence of explosives when digging with a conventional method, of sludge or additives when using a tunnel boring machine with containment). Limestone materials can have a high potential for use provided that unsuitable materials such as those with high sulphate content are set aside. Conversely, molassic materials have a priori little potential for use.
The regulatory context mentioned in favour of waste prevention and recovery means that the management of excavated materials — in fact almost always in the context of major projects — is increasingly being considered at a very early stage. Indeed, at the very stage of the field surveys, the objective of which is to position the tunnel and to design the technical methods of excavation, tests are carried out on the materials taken to try to characterise them and to begin to foresee the possible uses and treatments (sorting, washing, crushing) that would be necessary.
The environmental assessment procedure imposed by European regulations further reinforces this trend: the environmental impacts of the project, assessed in the impact study, must be avoided, or if not reduced, then compensated for, in order for the project to receive a favourable opinion from the environmental authority and to be authorised. The environmental authority’s responses to recent major projects show the interest shown in waste management, particularly in terms of transport (encouragement to favour alternatives to road transport).
The purpose of these provisions is not so much to prevent impacts as to allow projects to be carried out with fewer environmental consequences. In terms of use, some of the excavated materials are reused on the site or evacuated for use in earthworks or as aggregate for concrete. However, as mentioned, the main use currently implemented is the use of inert waste as backfill for quarries. If the usefulness of this use should not be questioned, it highlights that the “loop” announced by the circular economy remains limited, far from a substitution to natural materials
The means to go further in order to reduce the environmental cost of projects appear limited. The development of new uses for waste materials, through innovation, is regularly discussed, but can we really go further? One probable cause of this limit to the “virtue” expected from projects is that urban construction is still completely apprehended according to a linear conception.
The building site as an urban mine?
However, the anthropocene context leads us to reexamine the operational methods of urbanisation: how do we develop? How do we build? The scarcity of resources and global warming will force us, in the relatively short term, to consider the space-time of the building site with even greater attention, because of the ecological and social upheavals it brings. We can hypothesise the need for a change of paradigm to develop the anthropocene urban space because one perspective could be to apprehend the projects through the materials they produce, no longer as waste but as resources. The construction site would then take on the value of an “urban mine”: the circulation of materials that it implies could be an opportunity that is seized to obtain secondary raw materials. By pursuing this reasoning, the production of useful materials could become a condition for justifying and authorising a major development project.
For further information:
Laëtitia Mongeard, « De la réglementation aux relations d’affaires, actions et instruments de publicisation de la gestion des gravats », Géocarrefour [En ligne], 95/1 | 2021, mis en ligne le 23 février 2021, consulté le 11 mars 2021. URL : http://journals.openedition.org/geocarrefour/16463
ibid, « De la démolition à la production de graves recyclées : analyse des logiques de proximité d’une filière dans l’agglomération lyonnaise », Flux, 2017/2 (N° 108), p. 64–79. URL : https://www.cairn.info/revue-flux-2017-2-page-64.htm
