Bigger and faster

The tunnelling sector worldwide seems to be going from strength to strength. High profile high speed rail, metro and road tunnel projects tend to get the bulk of international publicity. It is understandable - these projects usually feature the biggest tunnels and the schemes have impact more on the local populations.

However water (waste, fresh and hydroelectric schemes) may actually be just as big a sector. Some of the tunnels involved may be as small as 1 m (or less) in diameter for local urban services, but they may also range up to 12 m diameter or more for large scale hydro projects - and some others account for huge lengths of tunnel work.

There is certainly an abundance of tunnelling work available in the world today. Perhaps the main problem facing the sector is that there is an ever-growing shortage of construction professionals and qualified, skilled and experienced workers to meet the needs of the industry.

TBMs

It seems that no sooner does a job get under way using the world's largest diameter tunnel boring machines (TBMs), than another contract is entered into to go even larger! In Europe two 15.3 m diameter machines are already under way on Madrid's M30 road scheme in Spain. One is the very innovative unit from Herrenknecht with inner and outer cutterheads which can be rotated independently. The other is from Mitsubishi Heavy Industries of Japan in joint venture with Duro Felguera of Spain.

These machines are so large that an Alimak personnel lift has been built into one of them (the Herrenknecht) to take workers from the bottom to the top of the machine. They were the world's largest TBMs - however they did not hold the record for long. Herrenknecht has now just completed the first of two 15.4 m diameter Mixshield slurry TBMs in China for use on a road project in Shanghai, and both should be under way by the year end driving 14 km of tunnel.

These enormous machines have been designed to work in soft ground. It had generally been thought that true hard ground machines capable of boring through solid rock may not reach such diameters because of the huge power requirement to cut through the harder strata - but they are already getting close.

Robbins from the US is currently building a 14.4 m diameter hard rock monster to work on an expansion to the Sir Adam Beck hydro-electric power plant at Niagara Falls in Canada. This machine is being constructed on site and is scheduled for completion in late summer/early autumn and should be well under way by the year end, while Wirth's big tunnel reaming unit at 13.4 m - known as a TBE (Tunnel Bore Extender) - is currently completing the second Uetliberg road tunnel in Switzerland through medium strength Swiss molasse. The TBE is used to extend a pre-bored TBM pilot tunnel to the full dimension. Two slightly smaller versions are currently at work in Japan.

One important aspect of hard ground TBM innovation is in TBM cutter technology. Larger cutters tend to last longer which means a machine can run a greater distance between the slow process of cutter changing. Robbins, in particular, has been fitting most of its new large machines with 19 inch (483 mm) cutters rather than the 17 inch (432 mm) standard, and its new big machine for Niagara will be using 20 inch (508 mm) cutters for the first time. Robbins President, Lok Home, reckons “Judging by comparative results between 17 inch cutters and 19 inch cutters, we expect the 20 inch cutter to give an average performance of more than twice the life of a 17 inch cutter.”

China has been one of the real driving forces in terms of TBM purchase over the past few years, and now most of these huge machines are assembled locally. As an indicator of the strength of the Chinese TBM market, Rodney Craig writing recently in Tunnelling & Trenchless Construction magazine, reckons the number of TBMs in use there over the past six years as being in excess of 130 machines - and he feels that this is an underestimate.

The largest proportion of these machines (nearly 100) have gone into metro and road construction in Beijing, Shanghai and Guangzhou but there is considerable work ongoing in other sectors too. For example two Robbins and one Wirth 8.03 m diameter TBMs are currently involved in driving over 60 km of an 85 km long water tunnel in Liaoning Province to help improve water supply to the province's chief city of Shenyang.

Drill & blast

Conventional tunnelling using drill & blast equipment is often overshadowed by its TBM rival, in part because of the complexity, size, cost and visual impact of the modern large-scale TBM. However, in reality, probably more sections of road, rail and hydro tunnel are still driven by drill & blast than by other means, and the major manufacturers in this sector are making substantial improvements in drilling technology to keep up with their TBM counterparts.

Rigs are getting bigger, penetration rates are being improved and the modern drill rig is capable of drilling virtually as large a tunnel from a single machine as the largest of today's TBMs. But, where high speed or even greater tunnel width is essential, it is also possible, in a big tunnel, to use two drill rigs side-by-side thus extending size and advance speed capabilities.

Interestingly, at the recent Intermat exhibition in Paris, the world's two leading manufacturers of underground drilling equipment - Atlas Copco and Sandvik - both launched two very high capacity twin boom drill jumbos. Atlas Copco's new Rocket Boomer E2 can drill a tunnel of over 13 m in width and 9 m in height, while its 3 boom XE3 derivative - the first production models of which are working on a road tunnel project in Norway - will be able to drill to dimensions of 18 m in width and 13 m in height.

Sandvik Tamrock's new T9i twin boom machine has a reach of up to almost 15 m in width. No figures for a three boom version have yet been announced. Both these machines are fitted with high speed drifters and the latest drill automation technology whereby rounds can be programmed into an onboard computer and drilled automatically.

High Speed Rail

TBMs are going into a large number of major projects all around the world. Europe is seeing its share of units and is the location for some of the world's most ambitious bored rail tunnel projects. The Alptransit tunnels in Switzerland are at the forefront of these.

The 35.2 km Lötschberg tunnel has been completed and is currently being equipped - although this was only partially bored, with a little over half constructed by drill & blast. This is dwarfed by the even more ambitious 57 km long St Gotthard tunnel which is primarily being built with two 9.58 and two 8.83 m diameter Herrenknecht TBMs, although two of the most critical stages - the ultra-deep Sedrun section and part of the Faido section - are being driven by drill & blast.

At Sedrun the tunnel elevation is accessed by a pair of 800 m deep vertical shafts which may soon form the basic access for what would be the world's deepest railway station at what is known as the Porta Alpina. Tunnelling work on the St Gotthard is now more than 60% complete.

It has also been announced that the next stage of the Alptransit - the 15.4 km long Ceneri tunnel, to the south of the St Gotthard, has now commenced its initial construction phase. This too will primarily be built by TBM.

But the Alptransit tunnels are only part of a hugely ambitious series of high speed rail base (at valley floor level) tunnels through the Alps. The Lyon-Turin and Brenner base tunnels, each requiring in excess of 50 km of twin tunnels - have passed through the initial planning stages and work is beginning on aspects of these too.

Spain and Italy in particular have both been heavily involved in tunnelling for the extension of their own high speed rail networks. The 26.7 km Guadarrama tunnels north of Madrid were completed in 2005; these were bored by two Herrenknecht and two Wirth 9.5 m diameter machines operating side by side from both ends.

In the south of the country, this year has seen the completion of the 7.1 km Abdalajis high speed rail tunnels bored by 10 m diameter Robbins-designed ‘Mitsubishi' double shield machines manufactured in Spain by Duro Felguera.

The 25 km Pajares high speed rail tunnels are now under way in the northwest of the country and here the 10 m diameter machines in use are from Herrenknecht, Wirth NFM, Mitsubishi/Duro Felguera and Robbins.

Italy too has seen a huge amount of tunnelling taking place on its high speed rail system, although here a variety of methodology has been employed including TBM, drill & blast and even tunnelling with hydraulic hammers - more popular in Italy than most other areas of the world. Indeco, Rammer and Atlas Copco hydraulic hammers are probably most in use for this purpose.

Most of Germany's high speed rail tunnelling projects are now nearing completion. The Herrenknecht-driven Katzenberg tunnel between Karslruhe and Basle is well under way. Tunnelling work on the UK's final London stage of the Channel Tunnel Rail Link has been completed. This latter was bored by one Herrenknecht, two Wirth, two Lovat and two Kawasaki TBMs and will bring the existing stretch of high speed line into a new terminal at St. Pancras in central London via Stratford - the designated site for the 2012 London Olympics - and the St. Pancras-Stratford section will play a key role in transporting people to the main Olympic venues.

This project demonstrated an interesting crossover from surface construction technology in the use of modified Gomaco slipform pavers to place the trackbed and ancillary concrete structures. The speed of placement achieved using this technology makes it an impressive option for equipping major lengths of tunnel.

Northern Europe is not being left behind - particularly in Sweden, where the Bothnia Line continues with all the numerous contracts on this using drill and blast, while the resurrected Hallandsas tunnel is being driven with a Herrenknecht TBM.

North America doesn't see much rail tunnelling nowadays. However in Manhattan funding now seems to be coming available for some exciting rail projects - notably the East Side Access route to bring the Long Island Railroad into Grand Central Station in Manhattan and perhaps also the impressively named ‘Access to the Region's Core' or ‘Trans Hudson Express' (THE) line to tunnel under the Hudson River which would improve main line commuter access from New Jersey to midtown Mahattan.

In Turkey, the Marmaray tunnel has recently started construction and this will bring rail traffic under the Bosphorus joining Europe and Asia. Here a Lovat TBM will be used on the 11 km of bored approach tunnels. The tunnel under the Bosphorus itself will be in a 1.8 km immersed tube.

Metro tunnels

Tunnelling for metro lines is usually relatively shallow and tends to require different technology from the often deeper and harder rock tunnelling requirements faced by high speed rail projects. In Europe there has been much metro tunnelling seen in Italy and Spain. In the UK a project to drive 2.5 km of twin tunnels under the Thames with a 6m diameter Lovat TBM has just got under way for an extension to the Docklands Light Railway, while in Lausanne in Switzerland a new metro line is being driven primarily with roadheaders and hydraulic hammers. Even the magnificent Moscow Metro is expanding too, with Lovat having just secured a contract for a new extension.

In the Middle East, Iran has been seeing metro construction in Tehran, Esfahan, Mashhad and Shiraz. At the latter NFM/Wirth machines started up last year. In Tehran three lines totalling 90 km in length and 40 stations are now in operation. Tehran Urban and Suburban Railway Company has in hand US$ 2.5 billion to construct Lines 3 and 4 and extensions to existing lines, for about 70 km and this plan has also been approved by the city council

New York has seen a fair amount of work in rehabilitating and rerouting lines and station accesses in the ‘Ground Zero' area and there is now the real possibility that the long awaited 2nd Avenue Subway will get the go-ahead. First contracts are likely to go out to tender this summer. This will partly be constructed by TBM, as will the 7 Line extension taking this metro line down to the west side Hudson Yards area and aid in area regeneration.

In Latin America, both Caracas and Santiago have been the scenes of major metro line extensions. The latter has been spending around US$1 billion on two new metro lines, for much of which the construction has been underground.

But it is in China where perhaps the largest amount of metro tunnelling is taking place as the country gets to grips with massive growth, huge urban population centres and the necessity of being able to move people within this urban environment. Beijing, Shanghai and Guangzhou in particular have been developing and increasing their extensive metro systems - sometimes using innovative tunnelling technology like the DOT (Double O Tube) machines made by Japanese manufacturers like Mitsubishi and IHI, which effectively drive two side-by side tunnels at a single pass.

Road tunnels

Road tunnel construction has also been continuing at a fast pace. Here most of the shorter tunnels are being constructed by drill and blast, but there has been a recent trend towards the ultra large TBMs capable of driving double road decks, or side by side carriageways in a single pass as in Madrid and Shanghai.

There is also the dual use SMART tunnel which is being constructed, using two 13.21 m diameter Herrenknecht Mixshields, in Kuala Lumpur. This is a combined road and stormwater tunnel, capable of being turned over fully to flood relief in times of exceptionally heavy rainfall. For most of the year it will be primarily a road tunnel. Tunnelling was completed on this in April this year.

In Norway there has been a considerable amount of road tunnelling to link major roads across fjords and improve connections to island communities. These include the world's deepest undersea tunnel at Eiksund which runs 287 m below sea level, to connect the mainland to a group of offshore islands, which is being driven by drill and blast as are all the Norwegian road tunnels currently under construction. At Eiksund a computerised Norwegian-manufactured AMV three-boom drill rig mounted with Montabert drifters (rock drills) is being used.

Italy and Switzerland have also both been improving their road networks substantially and this involves a fair amount of tunnelling, while in France the A86 ring road round western Paris is virtually complete as far as the tunnelling is concerned. This is one of the projects where a sufficiently large TBM drive has been used to accommodate a two-deck road system in a single tunnel. This tunnel is due to open to traffic next year.

In addition to the new developments in the primary tunnel driving units, there have also been parallel advances in ancillary equipment for support, guidance and surveying, mucking out, and safety during the tunnelling process and in completed tunnels, which are too many to mention here without writing a lengthy book. Overall, the tunnelling sector is booming worldwide as, in particular, today's necessity of speed of travel between and within population centres frequently requires the below surface option to be taken. This market strength is likely to continue for the foreseeable future.