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Tunnel boring head
Tunnel boring head in the process of creating the L9
A metro system says a great deal about a city. Dense and democratic, it’s one of the few places where people from all walks of life actually rub elbows and regularly share, however briefly, the same closed space. New York has its rattling, atmospheric subway and London, its Tube. Barcelona, meanwhile, has a relatively clean and efficient, if, at times, crowded metro. Now, with the inauguration of the first section of the line nine (L9), the city is taking a definitive step into the major leagues of underground urban transportation.
When fully completed, the new line will stretch for almost 48 kilometres, making it the longest line in Europe and the longest metro line in the world of entirely new construction. It is also the most expensive enterprise the Catalan government has ever undertaken. The original projected cost was €2.25 billion, but it will wind up costing €6.5 billion, according to a recent La Vanguardia article.
The L9 will run clear across Barcelona from Can Zam in Santa Coloma to the Zona Franca on to the El Prat airport, with its L10 branch line going from Gorg in Badalona to the Nova Estació Poligon Pratenc. While the first five of its total 52 stations opened in December 2009, the estimated date for the line’s completion won’t be until some time in 2014, according to the latest estimates.
“Tunnel builders know that you sometimes know when you’ll begin a tunnel, but you never know when you’re actually going to finish it,” said Henning Schwarz, director of the geo-technical and monitoring department of GISA, the Generalitat’s public company that manages all major public construction, including that of metro lines. He said security in construction always has first priority.
The challenges facing the tunnellers in Barcelona’s metropolitan area are daunting. They must bore through highly varied geology, ranging from solid rock to soft sand and everything in between. The route passes beneath both of the city’s rivers, and lies below sea level in areas by the port. The project must proceed with the utmost care as it digs beneath the densely populated surface areas of the city. “Everybody wants a metro stop near their home, if possible,” Schwarz recently told Metropolitan. “But nobody wants it directly beneath them.”
The concern is understandable, given the ground destabilisation that occurred a few years ago in the Carmel neighbourhood during work on extending the L5 metro line. Although the only structure that actually collapsed at the time was a car park, hundreds of residents had to be temporarily relocated as a preventive measure, some for almost two years. At any rate, the officials at GISA said that extreme caution is being used as they tunnel below Barcelona’s busy surface.
At times, the tunnelling process can sound like something out of science fiction. The tunnel-boring machines are mammoth state-of-the-art devices, some as long as 100 metres and weighing as much as a Boeing 747 jumbo jet. Four of the five machines at work in Barcelona were built specifically for the L9 and L10 project.
The huge machines, with drilling heads ranging from 9.4 to 12 metres in diameter, are designed differently according to the type of geology through which they must tunnel. When boring through rock, for example, the drilling head splinters the rock into chips and the same immense machine excavates the chips, which are later put to use as construction material. The multi-purpose tunnel-boring machine also builds the concrete walls of the tunnel, so that as the machine advances, the new tunnel is already complete 10 metres behind the drilling head. Remarkable as this sounds, the procedure is not without its drawbacks.
ssentially it means that the only way out for the machine is forward, given that once the concrete tunnel is built behind it, the tunnel’s diameter becomes smaller than the machine, making it impossible for the machine to back up. In this regard, something of a tunneller’s nightmare occurred in the summer of 2009, when one of the tunnelling machines ran into difficulty while chewing its way through the wet, soft soil of the Zona Franca, where it remained trapped for a number of months.
At least half of the new line will run through large tunnels, 12 metres in diameter and consisting of two levels, one track superimposed on top of the other. Although worldwide a few such two-level tunnels exist for automobiles, such as those of Paris and Kuala Lumpur, this is the first time such a tunnel has been used for a metro line. The superimposed tracks make it possible to introduce the platform area inside the running tunnel, thereby having smaller, more compact stations and saving space in the more congested subterranean areas of the city.
Furthermore, to avoid Barcelona’s many other subterranean infrastructures, it is necessary to tunnel at depths of up to 80 metres below the surface. Some stations, in fact, will have platform areas located 60 metres below the surface. Primary access to the deepest stations will be by high-speed lifts, each capable of whisking a maximum of 40 passengers up and down at a time.
Despite all the risks and difficulties, and the high costs of the project, it should be well worth it. In one swoop, the new line will connect the radial ends of all Barcelona’s other metro lines, as well as the trains of the Ferrocarrils de la Generalitat, Renfe and some tram lines. The new L9 and L10 will thus create a true grid network.
“At the moment, to make a metro connection, you have to travel into the centre of the city,” explained Schwarz. “But with the new line, you will be able to change practically at the fringes of the city. It will decongest the metro lines in the city centre, mainly the L1 and L5 lines, which are intensely crowded at rush hour. And equally important, it will reduce car and bus traffic in areas of the city where the metro hasn’t reached before.”
The new line will also incorporate innovative technology. For starters, it will be the first completely automatic, driverless metro line in Barcelona. So far, such driverless metros exist in only a few cities worldwide, such as Paris and Singapore. As demonstrated in Paris, automatic trains improve frequency and reliability and are likewise more economical to operate. To ensure safety at the stations, all of the platforms will be closed off from the track by platform doors.
“Consider it as a kind of horizontal elevator,” said Schwarz. “A hundred years ago, when elevators were invented, they had human operators. Nowadays, we can push the buttons on our own, and this is more or less the same idea with automatic metro lines.”
Numerous sensors and cameras inside and outside the trains will connect to a control centre, where human beings will monitor the automatic activity of the train. As experiences elsewhere have shown, an automatic train’s acceleration and deceleration is more balanced and stable than that of a human operator, and so leads to considerable energy savings and improved passenger comfort.
Finally, in keeping with the city’s love of design, each of the 52 stations of the new line is being individually designed by different architects. Metro passengers should thus get the full Barcelona experience.