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TUNNELLING & UNDERGROUND CONSTRUCTION

Barcelona is investing heavily in its metro system.

Aradical double deck train tunnel, 'tunnellising' of existing, very busy lines, and light rail shuttle services are all part of work under way on the Barcelona metro system.

Since 1995 the city has been spending Pta15,000M (£56. 5M) a year on new works. One third of this is funded by the national government and two thirds by the autonomous government of Catalonia, the Generalitat de Catalonia.

'From this year until 2005 there will be more spent, ' says Miguel Angel Dombriz, the Geralitat's subdirector for projects and planning.

Much of this money will go on the new 41km Line Nine works which cut across the northern edge of the city and will help link existing routes. Fortytwo stations will be built in its four phases.

The main focus of work over the last five years has been the upgrading of the older lines to European standards, conversion to fixed catenary power supply, and short extensions. This will continue, and the little 1m gauge 'valley line' - built by Englishman John Pearson in the 1860s - is being double tracked and put below ground.

This 140km long line is one of two suburban lines owned and operated directly by the regional Catalonian government. The city metro is operated by the Barcelona city authority.

An unusual solution has been proposed for Line Nine: a single 10. 9m circular bore divided into upper and lower halves. Trains would run one way in the top section and the other below.

Though possibly safer for trains, the reason for the division is not the track but the stations. These will have platforms which fit inside the large diameter bore, saving the cost of additional excavation at stations.

'And that is important, because we are forced to use a very deep route line across the city, ' says Dombriz. Major excavation for stations up to 70m deep would be prohibitive, particularly as they will be frequent, at 600m stops.

Barcelona has limited ground space, stretching only 10km by 10km. Mountains lie to the north and west and the sea is to the east. Dombriz says that for 80% of its route the new line will run under rising ground and must also dip beneath existing services and other metro lines.

Access to platforms and station services such as ticketing will be within 24m diameter cylindrical wells. Between five and seven high speed lifts running at 2m/s will transfer up to 30 passengers at time to platform level. Spare space in the tunnels will be used for services and train control equipment rooms.

First phase work, worth £450M, was let at the end of July 2001. It comprises three contracts to form a short stretch of line and two branches. A first 3km length in cut and cover will be done by a joint venture of Construcciones Rubau and Construcciones and Materialies y Pavimentos. It runs from Meridian Sagrera and includes construction of the shaft for TBM launches.

A 2. 4km branch towards Badalona will be done using a soft ground EPB machine by another joint venture between Dragados, Necso, ACS and Sorigue.

'We have both hard and soft ground in the city, ' says Dombriz. 'In the land near the Llobregat River delta, and also the Besos River, there is clay and other soft alluvial material. In the other direction the route passes into the rock of the mountains, granite and decomposed granite. '

A rock machine is more appropriate for this section and will be used on a 5. 4km stretch towards Santa Coloma. A big joint venture of FCC, Construcciones Publicas y Civiles, Obrascon, Ferrovial-Agroman, Copisa and Constructora Pirenaica will tackle this.

Three more sections of the route will be let as well, with completion due for 2007. The first phase completes in 2004.

While the Generalitat team looks forwards, it is also continuing work on line extensions closer to the surface. The latest for Line Three is a new threestation section 2. 5km into hills north west of the city, around the university area. Line Three is a subsurface route no more than 10m deep to the tunnel crown, and in places only 2. 5m down.

Main construction has been in 'false tunnel' a cut and cover method with a concrete arch roof often used in Spain. Typically, a top trench with a shallow batter is used down to about 5m and then diaphragm walls installed; excavation is made as far as the tunnel roof which is backfilled after it is cast. The tunnel below is then excavated and a floor cast.

The most difficult part of a three-year contract for joint venture contractors Dragados and Copcisa was a crossing under the Ronda highway.

The six-lane peripheral road was built for the Olympics in 1992. The first part was in soft quaternary clays which required a micropile umbrella, formed in 18m lengths with a 4m overlap. Steel arch support at 1m intervals was used over the 500m length with a 300mm double shotcrete layer.

'The middle section had about 100m long of decomposed granite rock that required drill and blast, ' says Dombriz.

Tunnel design was by consultant Riazu.

Work on the suburban rail Baix Llobregat presented logistical problems and the need for vigilance as diaphragm walls are installed 2m away from a line with 10 minute interval live train services.

Contractor Fomento has to have lookouts posted at 200m intervals to stop work.

The old run-down line was bought by Catalonia in 1972 and is getting sustained investment - its services are important for the greater Barcelona catchment that runs up the river valley.

'We are double tracking the single line gradually and where necessary putting it below ground, ' says Dombriz. He says the policy is to eliminate all of the 465 level crossings in the region.

The current contract, over 18 months, is for a 1. 5km section of line with 700m taken below ground through the village of Sant Andreu de la Barca.

Transition gradients of 300m are needed either side.

Preparation included clearing services and demolition of some buildings, partly to make space for an underground station. Designer Pedro Araujo de Antonio of consultant Riazu says this was perhaps easier to work on than the line itself, because the new track diverges from the old line for the station.

The 'tunnellised' track must run between buildings, close alongside the existing track. Construction involves building a 10m deep diaphragm wall by the old track and then another 5. 2m away to form a 7m deep box big enough for a single train track.

With the train diverted into the new box a second will be built where the old track ran to create a double track underground line.

Dombriz says villagers have been tolerant of the work, because they will see the two halves of the town connected for the first time.

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