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Madrid metro races for finish

TUNNELLING & UNDERGROUND CONSTRUCTION

As the first phase of the Madrid metro opened, work was already under way on the next phase, due to open in 2003.

After completing a stunning 56km of new working metro in only four years - 38km of it underground - Madrid is battling to repeat the achievement. By 2003 it hopes to have another 54. 7km of mainly underground line in operation.

As passengers stepped on to the newly opened metro in 1999, work on the next phase was already under way.

The small construction team is proud that the original line extensions came in at Pta5. 5bn (£21M) per kilometre, or £25. 6M counting only the underground line. Thirty-seven stations were built.

This compares with £108M per kilometre for the recent 18km Athens metro or £107. 3M for the shorter Paris Meteor line. London's admittedly difficult 16km Jubilee Line extension cost £260M per kilometre.

'And they took longer, ' points out Manuel Melis, the civil engineering professor who has been a driving force in the expansion programme. He is president of Metro de Madrid as well as directorgeneral of the transport infrastructure division in Communidad de Madrid, the regional government.

Melis, who is very hands-on, is assertive about what he thinks are the important factors in achieving speed and low cost. At the top of the list is safety and caution. What counts most, he says, is keeping the work moving and avoiding disasters.

'Delay and collapses cost money. Clients will pay almost anything to get stalled work going again. And contractors are good at exploiting that. Claims mount up. '

He concedes that perhaps Madrid has some advantages. Athens, for example, had special problems because tunnelling experience was limited and the archaeology was a nightmare. Compared with London and Paris, Spanish contract bids are cheaper and planning issues can be dealt with more quickly.

The routes also pass through less congested areas than in the other cities. For example, much of the second phase in Madrid is comprised of a new circle line linking five developing dormitory towns south of the capital. There is undeveloped land between them and also along part of the extension to Line Ten which will connect the 40km circle into the main city system (see box).

The streets above this 'MetroSur' are wide and relatively traffic free, buildings are mainly four or five storeys and, unlike London, there are no major river crossings to deal with.

But these are not the main factors. Madrid's work has had its own complexities. The first phase was mainly in the city centre, creating two new lines and extending others. The second stage includes city centre work too, threading an extension to the new airport line into the business district, where a check-in terminal is being built.

The soft ground which fills the Madrid basin is no easier than that found in other cities, being mainly alluvial sands and clays. Melis says that it is similar to London Clay in places, although with more sand lenses and perched water. And the decision to keep the lines shallow, at about 16m, to make the system easier and quicker to use, means there is increased risk of settlement damage. Melis says he is thankful for the 'marvellous' tool of compensation grouting.

Despite such tools, he begins with caution. He is vigorously opposed to large scale open face tunnelling in soft ground.

'I would absolutely forbid these methods whether it is NATM, pre-cutting or face stabilisation, ' he declares. 'I would not authorise it even in soft rock. '

NATM, he believes, is not only unproven but has such a history of collapses and failures that to use it other than for harder rock is 'criminal'particularly 'as you can put lives at risk' Pre-cutting and face support systems, like fibre glass rods, are also too time consuming and expensive, he says. 'Show me figures on rates of progress and cost that prove otherwise and I will consider them. '

Even then, he believes the science of soil mechanics is still too undeveloped to guarantee safety.

'A huge face 10m high or more could have major variations within it and you have to test all over. It's time consuming and expensive and still you might miss something. '

He believes the only solution is to use the now well-developed earth pressure balance tunnel boring machine, 'allowing you to keep a robust steel wall against the face at all times' Where the machine cannot be used or is not available, you should keep open face to a minimum, Melis says.

Madrid uses a variant of the Belgian hand excavation method, with timber shoring and boards supporting initially all but a 3m 2opening.

The top heading is widened cautiously, before concreting an arch and then working down. The bench comes out some metres back from the face for stability. The centre is then excavated before the two sides are dug out.

'The Phoenicians developed this 3000 years ago and you can achieve 2. 5m a day with it, 'Melis says, although he agrees that where the use of pneumatic hand-held tools is now facing restrictions, this may be a more difficult method to employ.

The extension to the new Line Eight airport line is being finished by the 'Madrid method' because the TBM that did the first 2km of the drive towards the city centre is now required on another contract.

Availability of machines has meant some juggling with methods.

But the EPB machine is the ideal. Melis says complaints about high initial costs are a false economy compared with the cost of long delays.

Madrid has even insisted on contractors buying higher specification machines. Bidders offering machines with 1500mt torque were told to go away and get 2000mt 'or they would not get the work' A new machine for the second phase from manufacturer Herrenknecht has 2300mt of torque.

Similarly, the machines were required to have 10,000t of thrust rather than 6000t. 'It costs nothing - 5% to 10% on the [cost of the] machine and you can just push your way out of trouble, ' says Melis.

Other 'certainty' features included doubling of the tail grouting pipes to avoid blockage and the risk of settlement from an unfilled annulus around the segmental lining. 'The philosophy is safety and redundancy, ' he says.

He also believes money should be spent without restriction on the relatively small expense of ground investigation and instrumentation. 'That way the engineering team has the best information for negotiating with the contractors as problems arise. No one pulls the wool over anyone's eyes. '

Madrid has built up 8000 measuring points on buildings and in the ground. Data is recorded using a variant of a GIS computer system with each instrument accessible by a double mouse click on a detailed map.

The team developed its own Windows-based software rather than bringing in expensive custom systems. Melis' colleague Ildefonso de Matias, who co-ordinates all the electrical and mechanical works, spent three months working on the software with programmers.

They both believe information is crucial for good, fast decisions. And fast decisions are critical to avoid problems, especially where costly lawyers might become embroiled. 'You have to try and foresee the problems and reach an agreement with the contractor even before it emerges, ' says de Matias.

'We try to make a decision within 24 hours, ' says Melis. This requires the best political back-up, and he says he is indebted to Communidad de Madrid transport minister Luis Cortes for fast and positive support. For example, when local residents objected to the location of a station, the team was able to change the line of the route in a day, he says.

Having a tight management structure speeds up decision making. 'Work is very simple if you have a clear idea of what you are doing, ' says Melis.

'You do not need layers of people, but direct communication and co-ordination. '

He thinks outside project consultants overcomplicate rather than solve problems, particularly where local engineers are skilled and experienced.

Madrid's new programme of extensions is costed at £1. 3bn against the £1bn spent on the first phase, but it will have fewer stations - 26 compared with 37.

However eight of these will be interchanges, compared with the four built in 1995-1999.

The extra cost is due to whole length being in tunnel (phase one included an 18km above ground suburban rail line built with the railway operator) and because depots are required for the new line. 'We didn't have to build any in the first section, ' says Melis.

Main elements comprise the 40. 5km loop of the MetroSur, divided into five major TBM tunnelling contracts and one smaller cut and cover job, the extension of Line Ten which will connect to the main system, and Line Eight to the airport. Exacavation diameter is 9. 4m while the final internal diameter is 8. 4m for the double track.

The MetroSur contracts all include sections in 'false tunnel' built between diaphragm walls or in open trench, some open cutting. But the majority is tunnelled by EPB machines.

On the Line Ten extension, one contract is tackling the 6. 7km of new line while another will widen the existing tunnel for higher capacity rolling stock.

Voltage is being upgraded to 1500kV from the 600kV used on the main system.

The final part of the programme is to extend the airport line. This was built from the airport inwards in the first phase but stopped short of the centre - passengers had to change on to an older line to complete their journeys.

A new 5. 9km tunnel brings passengers directly into the city centre, reducing the airport journey time substantially.

Two stations are included. One is a new interchange with another line and the other is a remodelling of the terminus Nuevos Ministerios, where the line will interchange with two other metro lines and four suburban train routes. The new station will also provide in-town airport check-in facilities like those available at Paddington in London and in Hong Kong.

TBMs from the first phase are being deployed on the work. They include three Herrenknechts and two Mitsubishi/NFM machines making the full size 9. 4m diameter and a smaller diameter Lovat working on a small section of single track double bore tunnel.

Hard compacted sand beds and some gypsum are the biggest problem for the drives on the MetroSur, as well as running sand. Geology is similar to Madrid itself, with perhaps more sand than the clay and sandy clay in the city.

'In general it's good and usually quite stable, ' says Frinciso Trelles from the contracting joint venture of ACS and Vias, which has the 30-month contract for the Alorcon section. This includes the large transfer station for the Line Ten link to Madrid.

'But the sand can be abrasive and some of the sand is running sand.

There is also quite a lot of water in some pockets but it drains out quite quickly. '

The 9. 43m diameter Herrenkecht machine erects a seven-segment precast concrete lining with a cement grout filling the annulus. Segments are 1. 5m wide and 320mm thick with a neoprene seal. Internal running tunnel diameter is 8. 4m.

Progress graphs for the MetroSur show good speed: the Herrenknecht machine on this job made 3000m in the first 245 days. That includes stops as it was brought through two stations.

Stations are built within diaphragm wall boxes with 'eyes' to allow the machines through.

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