The first line of the Paris metro between Porte de Vincennes and Porte Maillot was opened on 19 July 1900 for the Universal Exhibition of that same year. The 1889 Universal Exhibition had taken place at the same time as the opening of the Eiffel Tower. The “father” of the Paris metro, engineer Fulgence Bienvenüe, wanted his invention to make the French capital one of the most modern cities in the world. The following years saw the creation of more lines – numbers 2, 3 and then 4, which was a major technical challenge since it involved going under the River Seine. Each stage of the construction of Paris’ underground metro system, which covered an ever increasing area, required further technological innovations. The photo, which shows construction of Line 9 in around 1930, looks like it could have been taken in a coal mine shaft. The article below shows just how much tunnel excavation techniques have progressed since then…


Although the metro network in the city of Paris itself was already very dense, the urban development of the surrounding region, with its business districts, new towns and airports required a system that better connected the centre to its outskirts and the suburban areas between themselves. In 2010, the French parliament set in motion the process of transforming the Paris region into a world-class metropolitan area. A key element of this ambitious undertaking is a vast infrastructure project that includes the creation of four new metro lines (15, 16, 17, and 18). A public agency, Société du Grand Paris, is managing this new network, called “Grand Paris Express”. Rounding out this beltway metro project are the extensions to Lines 11 and 14 (Bouygues Travaux Publics carried out Package 2 of the north extension of the latter for Paris transport authority RATP) and the west extension of the RER Eole rail line for French railways operator SNCF Réseau.


The 33-km Line 15 South will run through 22 municipalities and provide transport to over one million people. Many of the stations on the line will connect with already-existing RER rail, metro, tram, and other public transport lines. Line 15 South will lighten the load on transport services running to the southern Paris metropolitan area and ease congestion on main roads, all while getting commuters to their destinations much faster. It will also improve access to major public facilities such as Institut Gustave-Roussy hospital at Villejuif, Musée d’art contemporain at Vitry-sur-Seine, and Henri-Mondor hospital at Créteil. It is set to come into service in 2025. By 2030, with the addition of the future west and east segments, it will form a 75-km beltway circling the capital.


Construction of the 68 stations for the Grand Paris Express project got under way with the work on the Fort d’Issy–Vanves–Clamart station (Package T3B), located where the municipalities of Issy-les-Moulineaux, Vanves, Clamart, and Malakoff meet. This project is complex because part of the underground structure had to be built beneath the tracks of Line N of the Transilien rail network, which connects Paris-Montparnasse train station to suburbs west of Paris, without interrupting service on these tracks. Horizon gave the contract for the earthworks to Tedelis, a joint venture between Bouygues Travaux Publics and Cosson, a Colas subsidiary. When the two tunnel boring machines arrive at their final destination in 2020 and 2021, they will be dismantled in an open area inside the Fort d’Issy–Vanves– Clamart Station.


Once the foundations of the future station were finished, a critical task awaited the consortium’s workers: shifting the reinforced concrete slab to close and cover the top of the structure. All their ingenuity was required to move a slab weighing 7,000 tonnes (the same as the Eiffel Tower) in an extraordinarily short 100 hours. This operation was carried out with great precision by the same partner that worked with Bouygues Travaux Publics at Chernobyl to slide the confinement shelter over the damaged nuclear power plant there. Bouygues Travaux Publics finished the excavation for the “station box”, a structure whose dimensions – 110 metres long, 26 metres wide, and 26 metres deep – are exceptional. The consortium will resume work on the structural elements once the tunnel boring machines coming from the east and west have reached their final destination, respectively in 2020 and 2021. At that stage, Bouygues Travaux Publics will add four floors to the station and put in the platforms of the future metro on the lower level.


Société du Grand Paris is taking multiple initiatives to limit the impact of disturbances on the daily lives of people living in the surrounding areas. One of these innovative measures is a “worksite forecast” that indicates the predicted noise level around the work area during the coming ten days. A module connected to noise sensors and a camera is used to locate noise sources. This new service, first installed at the Fort d’Issy–Vanves–Clamart Station, will be rolled out at all Grand Paris Express worksites. The Horizon consortium has also adopted this system. Sound barriers have been installed on the hoardings around the worksites of Line 15 South in order to absorb noise pollution. Personnel have also briefed on the need to keep noise to a minimum, and covers are always put over the equipment to reduce the noise from engines. To improve their performance in this area, Bouygues Construction and Colas have invested, through a Bouygues group intrapreneurship programme, in an innovative solution called Com’in. This AI-based tool is designed to analyse and manage in real time disturbances related to noise, dust, and mobility.


Located to south-east of Paris, Package T2A crosses five municipalities between Villejuif and Créteil. The work awarded to the Horizon consortium includes the construction of four stations (Créteil l’Échat, Le Vert de Maisons, Les Ardoines, and Vitry Centre), several related structures, 7.7 kilometres of tunnels, and the launch shaft for the tunnel boring machines on the Arrighi brownfield site in Vitry-sur-Seine. One particularity here is that the soil is varied and complex, thus calling for very special techniques to reinforce it. The Vert de Maisons station is located at the intersection between Alfortville and Maisons-Alfort, near the Paris-Lyon-Marseille high-speed rail line and RER D rail line, which will connect at this station with Line 15 South. Part of the station is being built under a group of listed buildings dating from the 1930s, a situation that has greatly complicated the work. Built with 74-m-deep diaphragm walls and using conventional methods for the foundation excavation, the Vert de Maisons station will require ground freezing and injection techniques to stabilise the soil.


On the brownfield Arrighi site at Vitry-sur-Seine, the consortium sunk a 50-m-deep shaft to launch the two tunnel boring machines (TBMs). The first, named Aby, began its westward drive toward Villejuif-Louis Aragon last June, while Marina headed eastward, toward Créteil l’Échat, in late December. These gigantic machines with an outer diameter of 9.87 meters and a length of 122 meters will tunnel, respectively, 4.3 kilometres and 2.8 kilometres at a rate of 12 to 16 metres a day, or 300 metres a month. Owing to the nature of the subsoil and certain geological conditions, a slurry shield tunnel boring machine was chosen for the excavation. “Compared with other TBMs, this model is better suited to high-permeability, low-density soil,” explains Benjamin Kitzis, Director of tunnelling operations at Bouygues Travaux Publics.


Package T3A is the extreme western section of Line 15 South that runs through the municipalities of Sèvres, Boulogne-Billancourt, and Issy-les-Moulineaux. The Horizon consortium is building 4.2 kilometres of tunnel, two stations, and several related structures as well as the shaft for launching the tunnel boring machine. The underground line will pass beneath the River Seine three times. Unlike for Package T2A, here the consortium is using an Earth-pressure-balance TBM. “Since the surface of the launch area is very confined, we didn’t have room to set up a slurry separation plant,” explains Richard Desvignes, Tunnel equipment manager at Bouygues Travaux Publics. And unlike with a slurry shield TBM, the excavated material is then transported by conveyor belt from the bottom of the shaft to barges on the Seine.


At the foot of the skyscrapers at La Défense, Bouygues Travaux Publics is digging a 6.1-km tunnel that will connect the La Défense business district to Haussmann-Saint Lazare railway station and then extend the RER E rail line to the west. A new station at Porte Maillot is also part of the project. On Avenue Gambetta in Courbevoie, workers have sunk a shaft over 38 metres deep to launch the tunnel boring machine. Called “Virginie”, the tunnel boring machine is named after Virginie Blivet, personal assistant to the Project director at SNCF Réseau. It is the largest machine currently in operation in Paris, thanks to its length of 90 metres and diameter of 11.1. It has been specially designed for this project being carried out in a very dense urban area with the support of a team from the German TBM manufacturer Herrenknecht. It advances at rate of between 8 and 16 metres every day. The Eole worksite is being carried out by a consortium led by Bouygues Travaux Publics, with Razel-Bec, Sefi-Intrafor, Eiffage Génie Civil and Eiffage Fondations, and is worth a total of €600 million.


Because of the nature of the soil along the alignment, Bouygues Travaux Publics opted for a slurry shield tunnel boring machine. With this type of TBM, pressure is maintained at the tunnel face by continually injecting a clay-based slurry called bentonite behind the cutterhead. The excavated spoil (muck) is pumped out from the TBM to a 180-m-long temporary installation through a hydraulic mucking pipe. Thanks to this system running the long distance across the suburb of Courbevoie, the need to have some 250 trucks a day to haul away the 1.3 million tonnes of spoil produced by the TBM is eliminated. In this closed-circuit system, the muck is transported by pipe to the “Base Seine” temporary installation, where it is filtered and processed in large tanks. The slurry is then sent back to the TBM to be used again, while the excavation material separated out at the plant is taken away by barge. This plant is able to process 2,500 cubic metres of bentonite per hour, a volume equivalent to that of an Olympic swimming pool. Located opposite Temple de l’Amour, a listed building on the Île-de-la-Jatte island, Base Seine had to be painted green at the request of Architectes des Bâtiments de France (France’s national heritage body).


“What’s stimulating about this project is the variety of work that must be done. Practically all civil engineering techniques are called into play,” says Project director Philippe Vaillant. The new Porte Maillot station is in itself a technical and organisational challenge. It adjoins several existing infrastructures, including Line 1 of the Paris metro, the RER A rail line, the car park of Palais des Congrès convention centre, the current station on RER C rail line, and the ring road around the city. Porte Maillot is one of the main gateways to the capital and an exceptionally dense urban environment. The station will have a six-level main hall open to the sky and covered with a glass roof and an underground station that will be 70 meters long and 15 meters wide. The building’s construction beneath Port Maillot roundabout will call for the installation of diaphragm walls 35 to 53 metres deep. The station will also contain halls for connections with RER C rail line, the Palais des Congrès, and Metro Line 1. It is scheduled to open to the public in 2022.