Innovative bridge construction and rail laying technologies are being deployed in southern France to speed construction of the new Bordeaux-Tours high speed rail line. Mark Hansford reports from Poitiers.
After barely three years of construction, civils work on the 302km long Bordeaux-Tours high speed rail line through south western France is now 90% complete.
And the pace will not slow as the project moves into its railway systems phase - track laying, overhead line electrification installation and signalling.
We have used innovative project management methods throughout to make sure we get on with it
It’s all down to innovation. Innovation and determination. And both stem from the private finance model that is being used to build the project. So says Laurent Cavrois, president of project concessionaire Lisea.
“We have to finance and build this railway and then operate and maintain it for 44 years,” he explains. “We have a 50 year concession, six years of which will be construction.” And as Lisea doesn’t start recouping any of its investment until it starts charging passenger and freight operators a track access charge, Cavrois says speed of construction is vital.
“We have used innovative project management methods throughout to make sure we get on with it,” he says. “It is a remarkable technical project.”
There has also been determination to overcome obstacles without delay, says Gilles Godard, chief executive of delivery consortium Cosea. Led by Vinci, the consortium includes Ineo Rail and Systra.
Determination was vital in getting the project back on schedule after a delayed start in February 2012 due to environmental challenges and land acquisition problems.
“We have already jumped over a number of hurdles,” says Godard. “We started about six months behind schedule and also had weather troubles. But today we are back on track. And that’s in particular due to the infrastructure team who have been organising at times 1,500 people on site.
“The earthworks are now pretty much completed,” he adds. “There are 10 or so significant structures on the route which will be completed by the end of this year or early next year. And in parallel with this we are setting down the base layers for the railway so that this summer we can essentially start with the rail works.”
It’s quite remarkable progress given that it is not a year since French dignitaries gathered near Bordeaux to see work begin on one of the biggest structures on the line, the Dordogne viaduct (NCE 13 June 2013).
And, while a hefty injection of resource in terms of operatives employed has played a large role in this rapid progress, the key has been innovation.
The project has been littered with technical innovations that have aided the programme. But two stand out.
The first has been used to speed construction of one of the larger structures on the job - the Auxance viaduct.
We employ our own designers; the design is driven by the construction; and that is driven by the needs of the concession
Here, an impressive temporary stay cable structure has been used to accelerate construction of the bridge’s simply-supported prestressed concrete box deck. “We are on the critical path. Hence the need for speed,” notes project director Gaetan Vigneras on the reasoning behind use of what is effectively a temporary cable stay bridge to build a bridge. “It is a system that has been used in France before, but it is technically very complex, as the span settles as you go.”
The viaduct, 450m long with 40m long spans, is a simply supported concrete box deck sitting 25m above ground level at its highest point on cast insitu concrete piers. Deck sections are installed a span at a time in a six day cycle, with three or four box segments installed per day.
Segments are precast in a central casting yard supplying deck segments to seven similar viaducts on the project. The yard will churn out 1,100 segments in all.
Once delivered to site the segments are stockpiled until needed. Then a specially designed transporter moves each 60t to 70t unit out onto the bridge. There, a temporary tower crane attached to the pier being advanced towards picks up the unit and sits it in position just in front of the last segment to be installed.
The crane holds the unit steady enough to allow temporary cable stays to be attached to the new unit while backstays are attached to the upper flange of the last span installed.
The tower crane then releases the segment and allows the next segment to be moved out ready for collection and installation. Once all sections on a span are installed, temporary prestressing cables are installed and tensioned and the temporary cable stays unhooked before the whole temporary cable stay unit is moved along one span and anchored in place.
It’s an impressive operation to witness; and it’s fast. “It allows us to build very quickly, but it demands a lot of planning,” says Vigneras. “The temporary cable stay system has all been designed and developed specifically for this project, and there is a very specific methodology.”
We have scale; we are putting our own money in. It’s risky. So we focus on the technical
Progress has been swift, with two masts in operation at any one time and two teams per mast working 6am to 6pm. “The difficult stage was getting off the ground,” explains Vigneras. “Once there, the whole process is industrialised and very smooth. The foundations started in spring 2013 and we will complete in September.”
It’s a bold approach, and one only likely to be used by a firm comfortable with taking - and managing - risk. “It’s a good innovation,” says Godard. “We made an early decision in the process to take this viaduct out and think of it differently.
“But we [Vinci] can do that,” he explains. “We have scale; we are putting our own money in. It’s risky. So we focus on the technical. We employ our own designers; the design is driven by the construction; and that is driven by the needs of the concession. So it allows solutions such as we are deploying at Auxance.”
The second innovation is about to be rolled into action, and is no less impressive. It is genuine cutting edge technology, having only been used once before - also on a Vinci-led high speed rail project.
Known as a “pusher” wagon for continuous welded rails, it allows the rapid, progressive construction of high speed rail lines.
Developed by Vinci subsidiary ETF, the system was used for the first time on France’s Est-Européenne high speed line last summer.
It rethinks conventional wisdom that construction of high speed rail lines entails installing a temporary track for trains carrying the concrete sleepers and the rails - often up to 434m long - that form the final track.
Source: © Pascal Le Doare´
On the Est-Européenne line the conventional approach was no good as logistical constraints required immediate installation of the final sleepers and rails.
A new method for laying the continuous welded rails had to be found. So ETF developed its pushing wagon. Unique in Europe, the wagon has two telescopic arms, each with 16t of tractive force for unloading the 400m-plus rails. The rails are thus extracted by propulsion, by “pushing”. In synchronisation a spider digger positions the rails on guides placed on the sleepers.
In total 412km of rails were laid this way, and the potential benefits to other projects were obvious. Thanks to the “pusher” wagon, it is no longer necessary to install a temporary track, yielding cost and time savings. And because the new rail line is laid directly in 400m-plus sections, it took only three days to lay the 42 rails stored on the train - that’s 8.4km of track. This process also presents substantial safety advantages by automating many manual handling operations.
Godard has now taken possession of the machine and will use it to lay half the tracks on the Bordeaux-Tours line, with the remainder being laid conventionally. It should significantly speed track laying. But having been used only once before, it is a move that is not without risk. Godard is comfortable with that.
“It’s a real innovation. We are using it now on the Est-Européenne line and we’ll use it here alongside conventional track laying methods. We’ll see if it works,” he says, nonchalantly.
It’s a risk. But with risk comes reward.
“At the end of 2016, we will be commissioning this railway with real trains and with real drivers,” says Godard. The line will enter service in 2017 - just five years after civils work began. That’s rapid progress.
Getting the finance together
Much has been made of the apparently hefty government subsidies that helped concessionaire Lisea raise the finance it needed to get the €7.8bn (£6.6bn) project to financial close.
Of the €7.8bn (£6.6bn) upfront investment required, €1bn (£800M) is coming from French rail operator RFF and another €3bn (£2.5bn) is in public subsidies paid by the state, local authorities and the European Union. Lisea itself is putting up just under half, or €3.8bn (£3.1bn). Yet much of this is also state guaranteed, with Lisea’s equity contribution a mere €772M (£634M).
But Lisea president Laurent Cavrois says that the subsidy issue has been overplayed.
“There is about €3bn of subsidy there. But the €1bn from RFF is not exactly a subsidy as it will get its money back. It’s the same with the loan from the European Investment Bank. So there is about 40% subsidy, but a good half of the financial risk is shouldered by Lisea one way or another,” he says.
This includes revenue risk.
“Cosea is responsible for designing, constructing, testing, operating and maintaining the line.
“But what differs this from other contracts is that we [Lisea] have a role to monetise and commercialise,” explains Cavrois. We have a responsibility to look after the operational and commercial aspects.
“It gives us a completely different role. We need to work alongside and coordinate with RFF as equal partners to develop the whole network. We’re keen to provide a service as well as develop a high speed network.”
Drawing distinct parallels with Britain’s high speed rail ambitions, Cavrois explains that the project is about far more than cutting the journey time from Paris to Bordeaux by one hour to two hours and five minutes.
“This is not only a high speed rail project. The existing line will be freed up, and a bottleneck north of Bordeaux will be removed, providing extra capacity to allow the development of freight and regional services,” he explains, “which is perhaps more what this project is about.”
RFF is anticipating an overall growth in traffic on the route of 20%, although predictions of growth - particularly freight growth - have been wildly wrong in the past.