Underground boom

24 April 2008

The Herrenknecht TBM for the Katzenberg rail tunnel is seen here at the company's manufacturing plan

The Herrenknecht TBM for the Katzenberg rail tunnel is seen here at the company's manufacturing plant.

Throughout Europe the Tunnel construction sector remains in good shape with major road, high speed rail, metro/light rail and water related tunnel projects proceeding at pace. Indeed the eyes of the world are on some of these projects due to their size and complexity.

For example, what were at a time the world's two largest soft ground tunnel boring machines (TBMs) - until an even bigger machine started up in China last month - have been working on a motorway ring road around Madrid in Spain. In Switzerland the epic St. Gotthard base tunnel (57 km in length and at its deepest some 2 km below the mountains above) is now over 65% complete, and the next stage of the eastern ‘flat' rail route through Switzerland to Italy is now starting up in the form of the Ceneri base tunnel to the south.

In the Nordic countries, most of the tunnelling being undertaken is by drill and blast for extending road and rail networks and for hydro-electric schemes. These countries are already seeing the employment of the latest developments in high speed, high capacity drilling equipment from the world's leading companies in this field - located in Sweden and Finland themselves.

Rail

One of the strongest stimulus for tunnelling in Europe has been huge investment in building new rail links, particularly in Germany, Italy, Spain and Switzerland. These projects have involved a considerable amount of tunnelling to keep gradients flat enough and curves gentle enough for the high speed trains.

Probably the most spectacular of these has been the Alptransit scheme in Switzerland. One major tunnel has been completed running from south of Basel through the centre of the country. This was the 34,6 km long Loetschberg tunnel for which most was advanced by drill and blast, but with significant bored sections. The latest state of this tunnel is that track laying has been completed and 80% of the catenary (power cables) has been installed. The tunnel is due to open for rail traffic in mid-2007.

The even more impressive Alptransit tunnel, though, is the new St Gotthard base tunnel - a base tunnel is one that runs at valley floor level - which is to the east of the Loetschberg and to the south of Zurich, Switzerland. As noted earlier, this will be some 57 km in length and will be the deepest civil tunnel in the world.

Part of the tunnel works, at Sedrun, have had to be accessed by twin 800 m deep shafts (themselves accessed by a 1 km long tunnel from the village of Sedrun) which, after lobbying by the local populace, will be used to access the world's deepest rail station known as the Porta Alpina. Tunnelling on the St Gotthard is already over 65% complete. Herrenknecht TBMs are being used for the bored sections while mostly Atlas Copco and Sandvik Tamrock drill rigs are being utilised on the drill and blast sections on the 9 m diameter drives.

This is an extremely complex project, not only because of the depth, but also because of very difficult ground conditions in some parts of the tunnel including squeezing ground in the Sedrun and Faido sections. The first actual TBM breakthrough was achieved between the Bodio and Faido sections in September, although the first TBM drive to be completed was in the Amsteg section in the mid-year. This is being continued through difficult rock conditions by drill and blast.

In Germany, much of the tunnelling for the country's extensive high speed rail system has been completed, but the longest of these - the Katzenberg tunnel between Karlsruhe and Basel - is still under way, again using Herrenknecht TBMs. The twin bored tunnels are just less than 9 km long - the longest on the German high speed rail network.

In Spain, the past year has seen the completion of the Guadarrama tunnels to the north of Madrid (driven by two Wirth TBMs and two Herrenknechts) and the Abdalajis tunnels between Cordoba and Malaga (with two Robbins designed Mitsubishi machines). Work has commenced on the Pajares tunnels in the north west with two Wirth machines, two Herreknechts and a Robbins/Mitsubishi machine. All are rail projects.

Italy is extremely mountainous with the Alps to the north and the Apennines down the country's spine so it has always been clear that any expansion of the rail network would require a lot of tunnelling. Some of the rock involved, though, is not too hard so tunnelling here has been mostly by conventional drill and blast means, or even with hydraulic hammers and roadheaders.

In the UK, the final underground section of the Channel Tunnel Rail Link into St Pancras Station in Central London is currently being equipped and is due to open next year. There is also the prospect of the Crossrail project which will cross under London from East to West. A preferred route has been decided, but there are still numerous objections and possible changes to be made before a final decision to go ahead (or not) can be made.

There are also some major heavy rail projects under way in the Nordic countries. Here most tunnels are driven by drill and blast - the Botniabanen line up the eastern side of Sweden is a prime example. There is much competition between the two big Nordic rock drill companies, Sandvik Tamrock and Atlas Copco and so far honours are pretty even with some contractors choosing the one and others the other on the numerous contracts which make up this route.

In the west of Sweden, advancing the Hallandsas tunnel is again being attempted. Previous work on this tunnel under the Hallandsas ridge between Malmo and Gothenburg was first undertaken with a TBM, which was a failure and was subsequently replaced by drill and blast. But major problems with water inflows, and poisoning of the groundwater by chemical grouts being used to try and control the water, led to this attempt being abandoned. Now another attempt is being made using a Herrenknecht TBM and specially designed segmental linings to cope with the high water pressures is under way, although progress is said to be slow at present.

In Finland too, the new rail tunnels for the Vuosaari port development are being developed by drill and blast. One of the largest construction projects in Finland, the expansion of the Vuosaari port, the new main sea trade hub for Helsinki started over a year ago and is expected to be finished in 2008. The related road and railway projects include some very demanding work. The longest tunnel, the railway, has a length of 13,6 km. The combined length of associated road and railroad work associated with the port project is 19 km of which 15,7 km is in tunnel.

Light rail & metro

There are numerous light rail and metro projects under way across Europe. In the north, Malmo's Citytunneln in Sweden is just getting under way with a Herrenknecht TBM. In the UK, the London Docklands Light Railway (DLR) is being expanded with another sub-Thames pair of tunnels to extend the City Airport line, with contractor Amec using a Lovat TBM.

In Lausanne, Switzerland an extension and reworking of its light rail system has just been completed. Here underground construction work was largely undertaken by roadheaders and hydraulic hammers.

In Spain extensions are under way on the Madrid, Barcelona and Seville Metro systems and a start is being made on the Malaga Metro, while in Portugal the Lisbon and Porto metro systems are both being extended.

In Italy there are major metro projects under way in Turin, Bologna, Rome and Naples. In Turin there was a double TBM breakthrough with two Lovat machines having their drives timed to break through alongside each other simultaneously - a unique event. Eastern Europe is also seeing metro expansions with work under way in Prague, Sofia and Moscow among others.

In Turkey, the Marmaray project - at least part of which is in Europe, will be extending Istanbul's commuter rail system under the Bosphorus. This project is one of the world's most ambitious urban transportation projects at the moment. The entire upgraded and new railway system will be approximately 76 km long. The main structures and systems include an immersed tube tunnel, bored tunnels, cut-and-cover tunnels, at - grade structures, three new underground stations, and 37 surface stations (renovation and upgrading).

Road Tunnels

Perhaps the most spectacular and ambitious urban road tunnel project being built in Europe at the moment is the upgrading of Madrid's M30 inner ring road with a number of major tunnel sections under construction on an accelerated programme. In particular the southern bypass section, which cuts off a corner of the existing M30 and which will substantially relieve congestion on the M30's busiest intersection, with the Motorway to Valencia, is particularly impressive.

Here what were, until recently, the world's two largest tunnel boring machines - one manufactured by Herrenknecht and the other by Mitsubishi Heavy Industries and Duro Felguera - have been driving a key tunnel section. The 15,2 m diameter Herrenknecht completed its drive in a time which the tunnel owners and contractors considered remarkable, while the MHI/DF machine got off to a bad start due to late delivery. However the latter machine is currently making amends with record progress for a TBM of this size and was expected to finish its drive by the end of October - around a month quicker than the Herrenknecht.

These two TBMs will be used on a new stretch of one of the Madrid outer ring roads, before being brought back to the M30 again for a northern bypass drive.

In the Alps, a second tube for the Tauern tunnel in Austria is to be commenced shortly. Following the Mont Blanc tunnel fire disaster there is considerable pressure to ‘double-up' several single tube tunnels to dual tubes, as two way traffic in long tunnels is now considered unsafe.

It should be said that there is little evidence that traffic accidents in tunnels are any more prevalent than open road ones. However, the confined space means if a fire breaks out the consequences can be horrendous - as was the case in the Mont Blanc tunnel in 1999, when 39 people died as the result of a truck fire. Considerable work is consequently being undertaken on analysis of the effects of tunnel fires and how to mitigate and extinguish them.

TBM construction is a relative rarity for European road tunnels as, for the most part, tunnels tend to be too short to justify the capital cost. Drill and blast is more typical and there are literally hundreds of road tunnels being driven by this method across the continent.

Norway in particular has been undertaking a huge programme of road tunnel construction, most notably up its spectacular, fjord-penetrated west coast. In such terrain, journeys can be very slow because of the need to either take ferries, or drive around fjords. There has also been a programme to build tunnels to offshore island communities and the world's deepest undersea tunnel at Eiksund, near Orsta is such an example - due for completion in 2008.

Here tunnel driving is by drill and blast using an Andersens Mek drill jumbo and shotcreting equipment. Volvo wheel loaders fitted with Gjerstad side-dumping buckets, off-loading into 20 or 25 tonne on-highway trucks are popular for mucking-out in Norway, although Caterpillar is making some inroads into this market with its range of wheel loaders - but also fitted with side dumping buckets for the most part.

Paris has seen the completion of tunnelling on the first section of its A86 ring road round the west of the city. Here one of the tunnels, for light vehicles only, is divided horizontally so contra-flowing traffic is handled one above the other, while a separate tunnel tube handles trucks and other heavy vehicles. The first section of this new road tunnel system is due to open next year. Tunnelling is continuing on the second section, which is due for completion in 2009.

Italy has also been driving a number of major road tunnels, particularly on Trans Appenine stretches of the trunk road network. Here drill and blast and hammer tunnelling is frequently used. In the far north east of the country, around Trieste, the main motorway system is being extended in tunnel to provide better access to Trieste's port and to neighbouring countries. Most of this is being undertaken by drill and blast, but a short urban section under housing and adjacent to a major hospital is having to be advanced by non-explosive means - mostly using hydraulic hammers and hydraulic excavators in the soft ground on this section.

Hydro Electric

Two important hydroelectric schemes involving a considerable amount of TBM tunnelling were under way in Europe in 2006. Karahnjukar in Iceland, where three Robbins hard rock machines are being operated, has now completed virtually all of the 39,5 km of the main headrace tunnel. Now TBM2 is being disassembled for work on the second, Ufsarlon, 8,7 km headrace tunnel.

In Austria, the Kops II pumped storage project is under construction with an underground power house being fed by pressure shafts from a headrace tunnel. Final breakthrough on the headrace tunnel was achieved in mid-2006. Here again a Robbins machine - this time an upsized rebuilt model which had previously worked in China, was utilised very successfully.

The Karahnjukar and Kops II TBMs were all using Robbins upsized 19 inch (483 mm) cutters which are now being employed on most of that manufacturer's high power machines with advantages claimed of more time between cutter changes and less blockages, leading to greater machine efficiency.

Future Prospects

Tunnelling is alive and well in Europe. With the prospect of more major Alpine rail tunnels being constructed in the near future - the Lyon-Turin and Brenner base tunnels - Europe will remain in the forefront of tunnelling technology - particularly as two major TBM manufacturers and both the biggest drilling rig manufacturers are located on the Continent.

Continuing urban population growth requires substantial infrastructure upgrading and the tendency is to move much of this underground as surface space is already occupied. This can be for roads, rail, metro, water, electric cables and, of course virtually every major European city needs substantial renewal and upgrading of its subsurface sewerage systems, which accounts for a huge, if unheralded, amount of tunnelling activity.

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