The period around 2014 and 2015 was a very bad time for civil engineering in France due to the financial crisis that has heavily impacted most of Europe. So says president of the French Tunnelling and Underground Space Association (AFTES), Michel Deffayet.

“French engineering companies had to rely on work abroad because there wasn’t enough available on the national and local level,” he says. “Over the last few years, however, the tunnelling sector started to grow significantly and it is now booming thanks to big upcoming projects.”

The trigger

The Grand Paris Express (GPE) has begun and is one of the biggest tunnel projects in the world. “We have never seen a project like this before,” says Deffayet. “It is a plan to expand the metro in Paris as the population is growing so fast. Some direct connections between suburbs are required, without the necessity of passing through the city centre.”

This project of EUR 35bn (USD 39.5bn) is funded with a new financing scheme including sales taxes for businesses.

The Société du Grand Paris (SGP) network is a 100% automatic metro system, with 200km of new railway lines, seven technical centres and 68 brand new interconnected stations.

Of particular note and designed by the architect Dominique Perrault, the Villejuif Institut Gustave-Roussy (IGR) station is one of the two deepest stations to be built on the GPE. A cylinder some 62m in diameter and 51m deep will be excavated to accommodate the nine levels of the IGR station. A multilevel interconnection hub between two perpendicular lines: 14 and 15 south will be required.

Four extensions will be excavated without blasting to house the platforms of the lines.

Deffayet explains, “The construction of IGR is one of the most challenging works in the SGP programme due to the geology. The IGR station is sited on a former sand quarry, which has been subsequently filled. Such heterogeneous formations might interfere with the construction of the large diaphragm wall that will surround the shaft. The diaphragm will be 640mm thick and it will be doubled by a reinforced concrete wall of 800mm up to 1.6m thick as the excavation progresses. The geology consists of alternating silty sands, marls sometimes very plastic, hard or altered limestone; and several groundwater tables are superposed separated by clayey levels.”

The first section of SGP underground network needs to be ready for the Olympic games in 2024 while the final section is scheduled to be complete in 2030.

  • Line 15 (south, west and east) will create a new ring route around Paris with 36 stations for a length of 33km (plus 3.7km for connection to the two maintenance sites). This line is estimated at EUR 5.9bn (USD 6.67bn). On the Line 15 south all of the lots have been already awarded. Eight Herrenknecht EPBMs of 9.87m diameter are expected to start working by the end of the year. One lot of this line will use a variable density machine. The contracts for Lines 15 west and 15 east are not awarded yet.
  • Line 16 has nine stations and a total length of 25km while the line 17 has 6 stations for a total length of 21 km. The cost for the awarded contracts of both lines is more than EUR 3.3bn (USD 3.74bn). Four Herrenknecht EPBMs and two Creg TBMs are expected to start working over the next months. Other TBMs will be selected and put at work for another lot, which has not been awarded yet.
  • The Line 18 with its 10 stations and a total length of 35km is estimated at EUR 2.9bn (USD 3.28bn). This line will be partly at grade.
  • The extension of the existing Line 11 with its 10 stations for a total length of 16km is estimated at EUR 1.3bn (USD 1.47bn) for the first section at Mairie des Lilas-Bois Perrier.
  • Extensions of the Line 14 (south and north) with its 12 stations for a total length of 21.5km are estimated at EUR 3.8bn (USD 4.3bn). The northern section, from Saint-Lazare to Mairie de Saint-Ouen, is nearly ready and the two TBMs have completed their drive. One TBM was an 8.92m diameter EPBM supplied by Herrenknecht, while the other was an 8.91m diameter EPB supplied by NFM. The commissioning of this north section is scheduled for the summer of 2020 while the southern extension will require the simultaneous work of three TBMs. The risk of encountering underground old quarries is very high in this section.

All the lines are situated amongst the Parisian multilayer geological profile. The longitudinal layout is mainly positioned in limestone, but stretches and crossings through plastic clays or sandy levels have been unavoidable. Another issue is the presence of old underground quarries within the good limestone.

Deffayet says that 14 TBMs are being put at work in Paris in 2019 and the number will increase. The peak is expected in 2020-2021 with 20 TBMs for SGP and another couple of TBMs for other ongoing projects in Paris, such as the extension of the RER E Eole.

“We are excited because we have never seen so much tunnelling activity in one city,” he adds. “The national tunnelling market is usually around EUR 500M (USD 565.8M) every year, but it will be triple this for the coming years.”

Massive workload

The industry will face a major challenge in managing this amount of work at the same time and in the same place, says Deffayet. “If we have 20 TBMs working at the same time, we need to get skilled staff to work on each and to complete the job on time.”

François Renault, tunnels technical director for Vinci Construction Grands Projets adds that Vinci has initiated some internal training programmes to train its staff. “This is a way to limit the amount of staff hired from external companies; the GPE is the opportunity for us to train young people,” says Renault. “When the GPE is complete, we can rely on these resources for projects in other countries.”

Among the other challenges related to the huge tunnelling workload in the coming years, is the question of urban congestion and the spoil issue.

“In the tenders that we received from SGP, they put a lot of emphasis on the impact of the work on local residents,” says Renault. “So we try to limit the impact of road transport within the city by finding special routes for our trucks. On top of this, we are exploring solutions to limit the noise generated from our jobsites.”

Depending on its chemical composition, the muck has to be placed at some dumpsites. Once extracted from the tunnel, the muck is kept in several pits and is subject to a chemical analysis by batch. After getting the results of the muck, it will be dispatched to the store area outside Paris.

According to Renault a recent trend in the French tunnelling market is moving forward with environmental targets, like testing the spoil as it is brought out of the tunnel.

“Such trends have resulted in an improved environmental awareness compared to past projects,” says Renault. “At Vinci we are quite happy about that as it fits with our company goals.”

Types of infrastructure

Deffayet explains the French infrastructure development programme mainly includes rail and metro work.

“We have to improve the capacity and connectivity of existing lines,” says Deffayet. “Some underground new high speed trains tunnels are planned but not in the short term.

“The metro sector is going really well as there is a huge demand from a number of cities, such as Marseille (the southern extension of Line 2 will see six new stations for a length of 5km), Toulouse (the new Line 3 with 21 stations and 27km), Lyon (an extension of Line B of 2.4km and the new line E with seven stations at 6km).”

As for road projects, work is only for refurbishment and other maintenance of existing infrastructure, as France’s road network is considered sufficient by the government.

In terms of hydropower, the Livet-et-Gavet project in the Alps has recently completed. It includes an almost 10km-long tunnel for a cost of EUR 350M (USD 396M). Two 4.74m diameter Herrenknecht TBMs excavated through hard metamorphic rock (mainly gneiss). The tunnel will carry the water from Livet’s dam to the Gavet power plant. From the upstream construction site, the first TBM bored 3km towards the Gavet plant while the second TBM drove upstream towards the Livet dam for 6.3km. The TBMs completed excavation at the end of 2017. The commissioning of the new plant is scheduled for 2020.

For high speed rail, the Lyon-Turin link is a 270km long railway line, 70% in France and 30% in Italy. The cross-border section includes a 57.5km-long tunnel with two tubes. The construction cost of this tunnel in estimated at EUR 8.6bn (USD 9.7bn). To present, at the French side in Saint-Martin-La-Porte (Savoie), more than 64% of the 9km first stretch has been dug. At the Italian side in Chiomonte, excavation of the 7km-long tunnel was completed in February 2017. Commissioning of the base tunnel is planned for 2030 but some political issues in Italy are still ongoing.

Another significant underground project is the underground nuclear waste laboratory being promoted by Andra, the French nuclear waste agency. The Cigeo underground laboratory, constructed at a depth of nearly 500m, has a network of 1.8km of tunnels. This is not a depository area and no nuclear materials will be brought here. The aim of this complex underground work is to study the behaviour of the Callovo-Oxfordian clay (argillite) that could host the future storage site, and to test in-situ all the procedures and methods that will be used for the storage. An important point is to see how the porosity and surrounding ground permeability of the ground might be affected by the construction and operation phases, and to demonstrate that the high thickness of the clay layer will protect against any nuclear propagation for millions of years.

Once all the tests will be done, the government will have to give the green light for the waste depository. The nuclear activity waste should then start the first phase of the final deposit system. The preliminary Cigeo project established that the nuclear waste will be transported on a ramp of 5km. Each package will be stored in the tunnels. The cost of the CIGEO radioactive waste storage facility is estimated at EUR 25bn (USD 28.2bn). Deffayet says that if the timetable of all upcoming projects is respected, the average of tunnelling activity will stay at a very high level for the next decade.

Opening up the market

“In the past the French construction market was not so open to foreign companies, mainly because of French contractual practices, which make it difficult for a foreign contractor to work without a French partner,” says Deffayet. “But the volume of upcoming projects requires the involvement of many companies just to stay in the time frame. Thus, we have now foreign companies involved in many cases.”

“The main French companies involved in the present tunnelling effort are Vinci, Bouygues, Eiffage, Demathieu Bard, NGE, Razel-Bec, Spie Batignolles. In the Grand Paris Express programme, they sometimes co-contracted works with foreign companies from Italy (Salini-Impregilo/ Pizzarotti), Switzerland (Implenia) and Belgium (Franki Foundations).”