By Lynda Myer
As it was revealed in NCE’s Tunnelling Festival, in order to dominating complex site issues on the Grand Paris Express project, Vinci Construction tested a tunnel boring machine (TBM) bridge and vertical shaft sinking machines (VSM) as the new innovations.
According to Thomas Lacour’s (Vinci Construction Grands Projets operations manager) speaking at the event on 7 December: “Villejuif-Institut Gustave Roussy Station was one of the most challenging stations to construct as it has two lines crossing it – line 14 and line 15.”
Including construction of 200km of new line for the city’s metro network, this Grand Paris Express project’s value is €35.6bn (£30bn). Also the developing process of Line 14 is undergoing, and lines 15, 16, 17 and 18 are new ones being added.
While the number of projects that Vinci Construction is delivering on behalf of project promoter Société du Grand Paris (SGP) is two packages, the Villejuif-Institut Gustave Roussy Station is one of the biggest in Vinci Construction’s TC3 package, which covers works on the southern part of line 15.
Located in the Hautes-Bruyères departmental park, the station is characterized by its cylindrical shape and May 2018 is the date of completing underground walls construction.
Commenting on the size of the station, Lacour said: “It was quite a challenge to build it, because it’s a very wide hole of 65m in diameter. It’s all made with cut and cover and it’s 55m deep.”
Considering the size of the station, initially cut and cover method was used by team and then they commenced the excavation and then did the inner lining going down. Lacour explained this was necessary to hold the station’s circular shape.
Additionally, Lacour noted that the site team was encountered with a major challenge that was specific to this site.
Improvising a way of transporting TBM Alison, which is responsible for excavation of a portion of the line 14 south extension tunnel, from one side of the station digging to the other, was necessary due to that the line 14 crosses over the top of line 15.
“We couldn’t wait for line 14 to finish excavation, so we decided to go on with the excavation and use the definitive structure that will be used for line 14 to carry across the TBM. The TBM is bigger than the trains, so it doesn’t fit. So, what we had to do is jack the system on hydraulic jacks to lower the definitive structure,” stated Lacour.
He also added: “Building the bridge to take the machine across was a challenging task because the TBM is heavy and they had to be careful with the definitive structure.”
Considering the location of station site which is very close to the Gustave Roussy cancer research hospital, the team also had to be very careful about deformations created by the tunneling and excavation works.
Moreover, the other innovation trialled by Vinci Construction was the use of VSM technology to construct four ventilation shafts between 8m and 12m wide and around 50m deep on line 15.
Comprising of a shaft boring machine and a lowering unit, the VSMs developed by Herrenknecht have two main components.
Explaining the machines further, Lacour said: “You have a cutting head on the bottom with a telescopic boom. It’s all done in slurry so you can take the slurry out to carry on. The segments go on as you dig down.”
He also noted: “Normally, the geology of Paris – characterized by limestone, sand, clay and gravel layers – lends itself to the cut and cover method. But since the team had 20 of these shafts to build and did not have enough machines to carry out cut and cover work at the same time, it tried out VSM as an alternative.”
Although the VSM technology worked, the costs did not.
“Unfortunately for us it was more expensive. We had a big learning curve at the beginning, we had to get used to it. So, it was more expensive in the end than a cut and cover. Despite this for future works VSM could be a big opportunity,” said Lacour.
