Transforming mobility in Greater Paris: an engineering and social challenge

Technical challenges: build inside and beneath a dense metropolitan area

Building an underground transport system in such a dense urban area as Greater Paris is nothing less than a large-scale technical challenge. Digging beneath the region’s surface reveals an especially complex subsoil structure comprising sensitive clay, groundwater and old quarries, without forgetting the many networks snaking their way through the ground, such as sewer pipes, cables and underground transport tunnels. Every operation involving the subsoil must be carried out with extreme levels of precision to avoid undermining the integrity and solidity of the buildings and infrastructures on the city’s surface. In heavily populated urban areas, floor space is a rare commodity, so work must be performed in a way that minimises any disruption for local residents.

The logistical challenges in coordination colossal worksites

Thousands of workers and hundreds of contractors are working on several worksites across Greater Paris at the same time, around 20 tunnel boring machines are concurrently in operation, millions of tons of earth must be evacuated... needless to say, the Grand Paris Express project represents a daunting logistical challenge.

A matter of coordinating people and machines…

… and optimising workflows

Grand Paris Express needs to keep work forging ahead, while preserving everyday urban life. To avoid gridlocked streets across the city and prevent vehicles from jamming restricted-access areas, specific off-peak times have been introduced for delivering materials. A combined road, rail and river transport strategy for supplying materials and evacuating spoil is also minimising the impact on road traffic and the environment, bearing in mind that a ship with a 5,000 ton cargo means 230 less trucks on the road. Logistics hubs have been set up in strategic points across the region and are used as both sorting and transit centres for delivering supplies and removing spoil as part of a just-in-time approach, which reduces the amount of traffic at urban sites.

Environmental challenges: substainable construction

Although worksites generate CO₂ emissions, the project is designed to ultimately have a positive global impact on the environment. By 2050, the network is expected to reduce the amount of CO₂ equivalent by 14.2 million tons.[1]

Shrink the carbon emissions generated by the works

Société des Grands Projets, which is the public company in charge of designing and building the transport network, is paying special attention to the impact that construction work on the new underground rapid transit systems is having on the environment.

• Optimise the process for transporting materials

One of the main strategies for driving down emissions involves improving the process for transporting materials and spoil. Société des Grands Projets and its partners, including VINCI, are counting on a combined rail-river transport model to avoid the use of trucks [2] and thereby cut CO₂ emissions. 

• Build with low-impact materials

Concrete is one of the key materials for building infrastructures, but it is also responsible for producing around 70% of a worksite’s carbon emissions. Therefore, VINCI is promoting the widespread use of Exegy® low-carbon concrete, especially the Exegy® Ultra range, which can lower emissions by 75% compared to conventional concrete.

• Recycle and reuse spoil

The worksites within the Grand Paris Express project are expected to generate a considerable amount of spoil, which has been estimated at 43 million tons. The goal is to recover at least 70% of that material. To reach this target, Extract (a VINCI Construction subsidiary) is involved in the earliest stages of the worksite to determine the composition of the materials and their reuse potential, so that the appropriate recycling processes can be chosen. Once the inert soil has been sorted, it is reused to landscape quarries and brownfield sites, or injected back into the worksites after treatment, which avoids having to tap into new natural resources. Some of the spoil is also transformed into aggregates and reused to make concrete or build roads. VINCI subsidiary Eurovia is capable of providing end-to-end solutions where delivery trucks supply aggregates (especially aggregates containing recycled materials) before returning with a full load of spoil, as well as solutions for recovering certain types of excavated material. These reuse and transformation strategies mean that the spoil is considered to be a resource in its own right, which demonstrates how the worksites within the Grand Paris Express project have adopted the principles of the circular economy.

Subtainable, energy-efficient infrastructures

The environmental impact of the Grand Paris Express project is not just restricted to the construction works. The subsequent operation of its rapid transit systems needs to embrace sustainability by anticipating the challenges posed by climate change. The Grand Paris Express stations and structures are designed to be energy-efficient. By way of an example, centralised technical management systems will be installed to improve energy consumption in the buildings and infrastructures. VINCI Construction and VINCI Energies have teamed up to create the innovative GreenFloor® HVAC system, which draws air into the concrete slabs before releasing it using both radiation and convection from the ceiling. This technology uses very little energy and provides substantial space savings.

The social challenges of a regional project

Grand Paris Express is more than just a major technical achievement, since the primary aim is to improve life for society by changing the very face of the city.

Restore balance across the region...

Some of the region’s outlying districts are affected by a lack of connections with the rest of the metropolitan area. The situation restricts their inhabitants’ access to employment, training, services and leisure activities. Grand Paris Express is delivering a tangible response to this issue by redesigning the connections between the region’s different suburbs and reducing the need to take journeys that run through central Paris. With its 68 new stations and interconnected lines, the network is streamlining travel and closing the distance that separates inhabitants from the job markets. For example, the time taken to travel between Noisy-Champs and La Défense will be halved from 70 minutes to just 35 minutes, while the journey between Palaiseau and Orly will be cut by a factor of four from an hour to less than 15 minutes.[3]

The new stations are also being accompanied by an ambitious urban redevelopment plan that involves creating new dynamic and sustainable districts. By 2030, close to 250,000 homes should be built near the new stations, together with shops, public amenities and green spaces. The aim is to promote a balanced development programme across the metropolitan area by creating attractive communities outside central Paris, ensuring that opportunities are divided evenly across the region and thereby reducing inequality.

...and forge stronger social ties

The sheer scale of the Grand Paris Express initiative is radically changing the living environment for the region’s inhabitants. This new form of mobility promotes social cohesion. The new districts built around the new stations include homes, shops, public amenities and green spaces, which improves social interaction and diversity. Projects are designed to encourage socialisation, with shared spaces, cultural centres and facilities to foster greater interaction between inhabitants.

Worksites driving jobs and employability prospects 

The work involved in leading the Grand Paris Express project is also powering the region’s economy by generating thousands of direct and indirect jobs in many different sectors. 

- 15,000 direct jobs in construction, engineering, project management, etc.

- 120,000 indirect jobs in urban design, retail, services, etc.

To ensure that the widest number of people can share in the project’s benefits, Société des Grands Projets has stipulated that 5% of all hours worked at the various worksites must be performed by people on back-to-work schemes. VINCI Construction is dedicating 7 to 10% of its worked hours to such schemes through the ViE programme (VINCI Insertion Emploi).

The success of such a project hinges on the ability to develop innovative technologies while meeting social and environmental ambitions. VINCI is contributing to the process by spearheading solutions that address the many different challenges, whether technical, logistical, environmental or social.

Sources

[1]Une nouvelle stratégie pour consolider les bénéfices environnementaux du Grand Paris Express (Société du Grand Paris, octobre 2021)

[2] https://www.vnf.fr/vnf/accueil/beneficier-de-solutions-en-faveur-de-la-transition-energetique-du-secteur-fluvial/flotte-fluviale-et-innovation/#:~:text=Le%20transport%20fluvial%20offre%20d,m%C3%AAme%20transport%20r%C3%A9alis%C3%A9%20par%20camion

[3] A bord du supermétro du Grand Paris : vos temps de trajet en 2030 (leparisien.fr, novembre 2018)