Pushing the limits

It is perhaps true of all human endeavour that attempts are always being made to advance technology, and tunnelling is no exception. Not only are more challenging tunnelling projects being undertaken, but the machinery being used to construct these projects is continually being advanced to enable tougher conditions to be attacked at higher speeds and at greater sizes. Meanwhile the ancillary equipment required to control all these improvements is also being developed to cope.

Bigger and better TBMs

While basic tunnel boring machine technology may not have actually made a great deal of progress over the past few years, the applications of this technology, and the ancillary equipment involved, have definitely been advanced significantly. This has enabled bigger machines to be developed to build even bigger tunnels at a single pass.

At the forefront of this technology advance on the tunnel boring machine (TBM) front have been key manufacturers Herrenknecht, Mitsubishi and Robbins. The former two companies are building ever bigger soft/medium ground machines, while Robbins specialises in hard rock tunnel boring technology and is doing the same in its sector.

On the soft ground side, the successful completion of the southern bypass section on Madrid's M30 motorway ring road, which opened in April this year, has been something of a revelation. The project used what at the time where the world's largest TBMs, at just over 15 m diameter. These were coupled with a tight schedule which involved not only the bored tunnels, but an incredibly complex open cut section too, making the project seem very optimistic.

In the event the optimism was well justified – and with a tremendous help from the exceptional performance of the two TBMs involved – one from Herrenknecht and one from Mitsubishi. Both performed hugely in advance of their contracted work schedules.

There were worries though – in particular with the Mitsubishi machine which was nearly six months late in being delivered on site. By the time the Mitsubishi was delivered and started boring, the Herrenknecht unit, which boasted central and outer cutterheads which could rotate independently of each other, had recorded some tremendous advance figures. It was nearing the completion of its drive, completing the 3.6 km section in eight months – a full month ahead of schedule.

But the Mitsubishi, manufactured by Duro Felguera in Spain, once it started up, completed its similar length drive through exactly the same ground, about a month quicker than its German rival. With boring speeds somewhat similar, it was quite possibly the Mitsubishi's segment handling system which provided the overall speed advantage enabling marginally quicker ring setting.

But, since the supply of the Madrid machines, Herrenknecht has gone one step further with two even larger machines assembled in China for the Chongming Island crossing near Shanghai. These two monsters were constructed and commenced boring in a remarkably short time. They are both 15.43 m in diameter (187 m²) and were finally fabricated under Herrenknecht supervision at the Shanghai Tunnel Engineering works in China.

However key elements of the machine, such as the cutterhead, main drive and key process instrumentation were first put together at the Herrenknecht head office at Schwanau in Germany. Interestingly Herrenknecht dispensed with its twin concentric cutterhead system for these machines despite claims that the cutterheads on the Madrid machine, which could counter rotate, could be used to balance the torque effect which could cause such a big machine to twist when full power was applied.

Meanwhile in North America, not to be left behind in the upsizing of TBMs trend, The Robbins Company – perhaps the longest standing name in the TBM sector – has supplied the largest ever hard rock TBM for a water diversion tunnel at Niagara Falls for a hydropower project. Unlike the soft ground machines, where upsizing to the next diameter has been progressed in centimetres, the Robbins machine is a massive 4.4 m in diameter bigger than its previous record holder.

This was also a particularly interesting TBM construction project. Contractor Strabag, in conjunction with Robbins, went for the use of an open main beam machine to be constructed entirely on site. This meant the normal factory assembly and testing, disassembly, transport to site and reconstruction and retesting on site was cut out, saving around three to four months on delivery time. The Rowa designed back-up was also constructed entirely on site

So far, after the initial running in period, the machine appears to be proceeding well. At the time of writing it had advanced around 750 m into its 10.4 km drive. It is fitted with Robbins' new 20 inch cutters which will mean more time between cutter changes and a corresponding improvement in machine availability and productivity.

Since starting work on the Niagara tunnel Robbins has also been awarded a Chinese hydropower tunnel contract where a 12.43 diameter TBM will be constructed on site – this time in an underground launch chamber. A similarly sized machine has been ordered from Herrenknecht too.

Bigger and better drill rigs

Not to be left behind in the upsizing trend, major drilling equipment manufacturers Atlas Copco and Sandvik have both been designing and launching new bigger and faster drill jumbos, capable of drilling large faces. Atlas Copco already has a number of its new L series rigs in operation on transportation tunnels in Sweden, Norway, and Finland.

One of the three boom configurations of this rig, the XL3 can drill a face of up to 170 m². Two units of the four boom version, the WL4, which can work on faces from 30 to 153 m² are already operating very successfully on the Nygard rail tunnel on Sweden's Bothnia Line rail project. The L series rigs are fitted with Atlas Copco's COP3038 high speed rock drill as standard and a new boom configuration.

Sandvik, not to be outdone by its rival, displayed a new three boom version of its i-series drill jumbo at Bauma – it launched as a single boom version at last year's Intermat – and this rig, designated the DT1130i can attack a face with a cross section of between 20m² and a massive 183m² and is equipped with the company's HFX5T high frequency rock drills.

Both the Atlas Copco and Sandvik rigs boast a high degree of automation, leading to great drilling accuracy which, in turn, means cleaner breaking and more rapid advance.

Road & rail

The highest profile tunnelling works today are undoubtedly the huge number of transportation tunnels which are currently under construction around the world. In addition to the Madrid southern ring road bypass tunnels and the Chongming island tunnels there is the Alptransit project in Switzerland. The 57 km long St Gotthard base tunnel (a base tunnel is one driven at valley floor level providing an almost flat route through a range of mountains), which at its deepest runs some 2000 ms below the mountains above, is now around 67% complete, while construction is just commencing on the next tunnel on the scheme, the 15.4 km Ceneri tunnel to the south.

The main Alptransit section, of which the St Gotthard rail tunnel is an integral part, involves a north-south rail route across Switzerland designed to take freight traffic off the country's road system, providing a high speed rail route between Italy to the south and Germany and the rest of the European rail network to the north. The tunnel is not the largest, but will be the longest rail tunnel when complete. However the huge depths involved and the difficulties experienced in the way of ground conditions make this a masterclass in tunnelling. It is being driven by TBM (all Herrenknecht) and by drill and blast depending on the type of ground.

Tunnelling is divided into five sections and tunnel driving has been completed on one of these – Bodio at the southern end – and is almost complete on Amsteg towards the north. Both of these are TBM drives. The deepest section, Sedrun, which is accessed by a pair of 800 m deep vertical shafts for a 1 km long horizontal adit, is being constructed by drill and blast and is proceeding well through dificult ground. This section will ultimately include the world's deepest train station, the Porta Alpina.

Americas

At long last, after budget related delays caused one of the contracts to be rebid, New York's huge transit tunnel programme appears to be getting under way. The first three projects to move ahead are the East Side Access project, bringing the Long Island Railroad into Grand Central Station, the Second Avenue Subway, originally proposed in 1929, but abandoned twice when funds were withdrawn, and the 7 Line extension. There are also plans for a new tunnel for the New Jersey Railroad under the Hudson River, bringing more rail lines into a new station to be constructed adjacent to the existing Penn Station and doubling commuter rail capacity between New Jersey and Manhattan.

Meanwhile, across the continent on Canada's west coast, Vancouver's Canada Line linking the city's international airport to the city centre is well on track. Here the stimulus for construction is Vancouver's hosting of the 2010 Winter Olympics and includes twin 2.45 km running tunnels being driven by a Lovat TBM.

Moving down the coast and across the border, Seattle is also constructing a Light rail system to the city's Sea-Tac airport while in California the long time coming high speed rail link from San Francisco and Sacramento south through Fresno to Los Angeles and San Diego, which will involve a considerable amount of tunnelling, is moving closer with design and environmental studies under way. Los Angeles is also expanding its Metro system.

South of the Caribbean, Metro Caracas is continuing construction with its Line 4 programme in the Venezuelan capital. Meanwhile in Sao Paulo in Brazil metro construction was interrupted when the wall of a shotcrete-lined shaft 40 m in diameter and 30 m deep collapsed, taking some pedestrians, a minibus and dumptrucks with it.

There are major transportation tunnel projects underway almost throughout Europe from north to south. Norway has an ongoing programme in place to improve transport infrastructure, particularly along its western coastline, and also with links to offshore islands.

In Sweden the Hallandsas rail tunnel is making slow progress as a TBM tunnel after its previous drill and blast development was halted following groundwater contamination and water inflow problems. Other rail projects are well under way, notably the Bothnia Line rail link up Sweden's east coast and the Malmo City tunnel, while Finland's Vuossaari road and rail tunnels have been under construction as access routes to a new port area for Helsinki.

Much of the tunnelling associated with the German high speed rail system has been completed as has the first Alptransit tunnel – the Loetschberg – in Switzerland, while ancillary tunnelling in connection with the Brenner base tunnel, which will be nearly as long and complex as the St. Gotthard rail tunnel, has started up in Austria. The French/Italian Lyon-Turin tunnel – another high speed rail base tunnel project under the Alps – has stalled for the moment and construction work has ceased.

The Spanish high speed rail system is also going strong and the past year has seen the completion of the Guadarrama and Abdalajis tunnels, but the long Pajares tunnel being driven by TBMs from Wirth, Herrenknecht (two each) and a Robbins-designed Mitsubishi/Duro Felguera single shield hard rock TBM is currently well under way. Extensions to the Madrid, Seville and Barcelona metro systems are in progress and work on a Malaga metro system has also started.

Italy too has a huge amount of tunnelling in progress or recently completed with road, rail and metro projects. An admittedly contrived occasion in the middle of 2006 saw the twin simultaneous breakthrough of two 9.4m diameter Lovat TBM driven tunnels on the Bologna Metro, while work in Turin, Rome and Naples systems is also ongoing.

Moving east, Europe and Asia will be linked by a rail system which will cross the Bosphorus in tunnel. The actual strait crossing will be in an immersed tube, but there is a considerable amount of associated rail tunnel works on both the European and Asian sides. Istanbul is also constructing a Metro system independent of the Bosphorus tunnels.

In the Middle East there is a fair amount of tunnel work under way on metro systems in several Iranian cities, mostly using TBMs, while the Dubai metro has just begun construction work.

Asia

China of course has been very much at the forefront of the tunnelling sector in Asia with probably well over 100 TBMs operating on road, rail water and wastewater work. Big metro systems are under way in a number of cities and, as with the Chongming tunnel mentioned earlier there are a number of schemes involving state of the art tunnelling systems in use. Beijing has a very comprehensive metro system in construction ahead of the 2008 Olympic Games, but this was set back recently by a station exit tunnel collapse in which six workers were reported killed.

2006 saw the opening of the 13 km long Hsuehshan tunnel in Taiwan, after a nightmare-ish construction. The tunnel was driven by a mixture of TBM and drill and blast through horrendous geological conditions. The project cost 25 lives, a TBM had to be abandoned and overall it took 15 years to build.

Th is year has also seen the breakthrough on the unique Stormwater Management and Road Tunnel (SMART) in Kuala Lumpur, Malaysia. This tunnel, driven by two 13.3m diameter Herrenknecht TBMs, is both a traffic and a water management tunnel. In normal conditions moderate floodwaters are carried through the lower section of the tunnel, while traffic continues to flow above it, but in severe flood conditions the tunnel is closed to traffic altogether and just used as a floodwater diversion tunnel.

Australia and New Zealand are both seeing a growth in tunnelling schemes for transportation. Sydney has had a number of recent tunnel projects completed, or under way, not always without controversy, while the Brisbane North South Bypass tunnel has just begun and tunnelling on the Perth Metro Rail twin tunnels under the City's Central Business District was completed in October.

Water system tunnels

Although transportation tunnels tend to have a high profile because of their interest to the general public, some of the longest and most complex tunnelling works involve water transportation – either for hydro electric purposes (as at Niagara) or for fresh or foul water movement. A major hydro scheme, for example, involving 70 km of tunnelling is at Karahnjukar in Iceland.

Here three Robbins TBMs have just finished driving the main headrace tunnels in some unexpectedly bad conditions with high water inflow and in weak ground. Even so, the machines finished pretty much on schedule.

In China, two Robbins and a Wirth TBM are driving the 80km long Dahuofang water tunnel to bring fresh water to one of China's otherwise poorly supplied major industrial cities. In the US the Arrowhead tunnels, which have proved another construction nightmare and involve 15 km of tunnels, are at last making some progress as part of the big Inland Feeder scheme to increase Southern California's water supply reliability in the face of future weather pattern uncertainties.

In India, Robbins has been awarded a major construction contract for two TBMs, conveyor system components, spares and cutters for a 43.5 km long 10 m diameter water tunnel which will be the longest driven tunnel with no intermediate access in the world to bring water to an arid area primarily for irrigation purposes.

But, probably worldwide, the biggest tunnelling sector of all is the largely unheralded work on wastewater systems. Either new systems are being put in place, or old systems repaired and expanded in line with increasing worldwide urbanisation and due to aging older sewerage networks. In the US alone it has been estimated that the cost of bringing the country's major cities' sewers up to scratch is around US$ 1.6 trillion over five years over what has been budgeted!

In Europe, similar problems are evident. London is now to get a 33 km, 7.2m diameter interceptor tunnel running under the River Thames at a cost of UK£ 2 billion (US$ 4 billion). Tunnels are very much at the forefront of all kinds of infrastructure development in our increasingly urbanised society. Construction is largely out of sight so the public is seldom aware of what is going on beneath the surface – which in turn has considerable benefits for the visual environment. On balance tunnelling is very much a key and growing sector within the international construction industry. IC