Tunnelling: Bigger and deeper

Tunnelling activity around the world continues to boom, with more and more high-profile projects getting underway. But while technology in the sector continues to improve all the time, a lack of skilled workers may put a brake on growth iC reports.

The tunnelling sector has boomed over recent years with the general growth of construction and the world economy. The highest profile projects are transportation tunnels, which continue to play a major role in bypassing over-congested urban areas - either with road tunnels, urban mass transit networks or high-speed rail links.

But there is also less obvious infrastructure. Sewerage, fresh water distribution, cable tunnels and hydroelectric schemes generate as much revenue for the tunnelling sector as the more visible and better publicised transport schemes.

The ever-growing potential for the tunnelling industry has now become apparent in mainstream construction. In one of the most significant events for the sector in the past year, April saw the world's largest construction equipment manufacturer, Caterpillar acquire Lovat of Canada, one of the world's top tunnel boring machine (TBM) manufacturers.

Like several of its competitors, Lovat was a family business founded by Richard Lovat and built by him, and his son Rick Lovat, up to one of the world's leading TBM manufacturers supporting a major factory expansion and the building of ever bigger and more sophisticated machines. Lovat was not top of the pecking order, but the takeover by Caterpillar with its huge financial resources has the potential to establish the company as a genuine major league player.

Rick Lovat will join Caterpillar with the brief to expand the company's tunnel boring business. "This acquisition is Caterpillar's entry into the rapidly expanding tunnel boring machine business, and it represents an excellent strategic fit for our companies and the customers we serve around the world," said Caterpillar group president Stu Levenick.

The Caterpillar-Lovat deal has by no means been the only change of ownership in the sector. Earlier, Norwegian Group Aker Kvaerner (now Aker Solutions) took a 50% shareholding in the second largest of the German TBM manufacturers, Wirth, although the main area of interest was Wirth's oil sector, maritime and drilling products. TBMs may not fit so easily in the Aker range of products.

Elsewhere China's Northern Heavy Industries (NHI) has taken a 70% controlling stake in former Wirth subsidiary, NFM, which is currently supplying a number of tunnel boring machines to China and elsewhere. NHI group company, Shenyang Heavy Machinery, was already the assembly partner for Wirth and NFM for TBMs destined for the Chinese market, as well as producing its own tunnelling shields.

Germany's bigger TBM manufacturer, Herrenknecht, has so far been king of the big league with the two largest machines to date currently reportedly making excellent progress boring twin 15.43 m tunnels on the combined tunnel and bridge link between Shanghai ‘s Pudong district and Chongming Island - China's third largest island. In April this year it is reported that Herrenknecht will now build an absolutely enormous 19m diameter TBM for a Russian construction company.

The big possible cloud on the horizon, though, is a shortage of experienced tunnelling engineers and workers. At one time it was possible to draw on people with at least associated skills from the then-in-the-doldrums mining sector, but a huge run up in commodity prices has been having the reverse effect pulling people back into the global minerals sector where salaries seem better than in tunnelling.

TBM mega projects

Notwithstanding the skills shortage, the tunnelling sector continues to see huge projects get underway. By far the most ambitious in the world is the huge Alptransit rail project in Switzerland where two separate north-south rail links are being constructed through the Alps at valley floor level (base tunnels). The first of these, the Loetschberg, was completed some two years ago, but the more complex new 57 km long St. Gotthard tunnel - the world's real tunnel mega project - continues. At the time of writing it was around 72% complete.

The final section to be started - the 7.8 km long Erstfeld (northern) section which had been delayed through a contract dispute, is now well under way. Of the five major tunnel contract sections, two are complete - Amsteg and Bodio - the drill and blast Sedrun section under the deepest part of the Gotthard Massif is over 70% complete. This section had to be accessed by a 800m deep vertical shaft system and the world's deepest railway station - the Porta Alpina - was to have been built. However this was put on indefinite hold last year when studies indicated substantial problems including the questionable feasibility of the elevators, the negative impact on tunnel rail capacity and the unprofitability of the whole enterprise. The remaining two tunnel sections - Erstfeld and Faido - are now being bored by Herrenknecht machines previously used respectively on the completed Amsteg and Bodio tunnel sections.

Meanwhile, the next major tunnel which would be part of the Alptransit project is now beginning to get under way. This is the 15 km long Ceneri tunnel, to the south of the Gotthard. Tunnelling on the main 2.3 km long access adit started up this year, driven by a 9.7 m diameter Robbins machine. However initial surveys suggest that only a part of the Ceneri tunnel is suitable for TBM construction and the greater part will be constructed by drill and blast.

TBM Tunnelling at the other big European mega project, the Karahnjukar hydro-electric scheme in Iceland, was completed in April this year when the last of the three Robbins TBMs completed its work on the Jökulsárveita diversion tunnel - its second bore after completing work on its section of the Headrace tunnels. Altogether the US$ 1.2 billion Karahnjukar project involved the construction of 72 km of tunnels, an underground powerhouse, five dams and will have a generating capacity of 4600 GWh a year - most of which will be used by the Fjardaál aluminium smelter, which is being built by Alcoa in the port of Reydarfjördur and is due to start up later this year.

China is probably seeing more tunnelling activity at present than anywhere else on earth, with some huge urban transportation projects under way. The tunnel/bridge connection between Shanghai and the island of Pudong in the Yangtze estuary is one of the largest - not least because of the size of the Herrenknecht TBMs being used in its construction. Once the most rural area of Shanghai, Chongming Island is now the subject of a major urban and agricultural master plan. With the construction of the tunnel link, the island is expected to increase in population while incorporating specialised agriculture in a sustainable design. It is also a major relocation centre for people relocated from Three Gorges Dam area.

Since late 2006, Herrenknecht's 15.43 m diameter tunnel boring machines - currently the world's largest diameter machines - have been at work at depths of up to 65 m and maximum water pressures of 6.5.bar. The project is on a colossal scale - about 1500 people will be employed at the large construction site, 2.7 million m3 of earth will have to be removed and approximately 7500 segmental lining rings installed. It is expected that the first gigantic TBM will reach the target shaft on Changxing island, on the Yangtze river, at the end of 2008.

In India, onsite assembly of a 10.0 m Double Shield TBM has been completed in Andhra Pradesh. A ceremony was held on March 18 to mark the official launch of this Robbins machine-the first of two TBMs to bore a 43.5 km long water tunnel for the Alimineti Madhava Reddy (AMR) Project -the world's longest tunnel without intermediate access. The project will transfer surplus water from the Srisailam Reservoir to the plains of the Nalgonda District for the Andhra Pradesh Government

The second Robbins machine will be assembled onsite later in 2008 and launched from the opposite end, at the inlet portal. After excavation of the entire tunnel is completed, a drilled and blasted disassembly chamber will be used for removal of each TBM and back-up.

The city of New York is set for some big tunnelling projects over the next few years - notably the 2^nd Avenue subway, the 7 line extension and the US$ 6.3 billion East Side Access project to bring the Long Island Railroad into Grand Central Station. The TBM drives on this ambitious project are going well, although potential delays in the construction of the new cavern excavation under Grand Central Station may put the finish date of the project back six months. The two 6.6 m diameter TBMs have been supplied by Robbins and Italy's SELI (which supplied a rebuilt Robbins machine)

The on-again, off-again, US$ 3.8 billion 2^nd Avenue subway has had political and financial problems in the past, but looks like it may get under way at last. But, as always with this project, which has been started twice before, funding could still be a problem.

The scheme will include a two-track line under 2^nd Avenue from 125th Street to the Financial District in Lower Manhattan. It will also include a connection from 2^nd Avenue through the 63rd Street tunnel to existing tracks for service to West Midtown and Brooklyn, along with sixteen new stations. Work is currently focused on relocating utilities along the first phase section prior to the arrival and launch of a TBM.

The third major New York tunnel project is the 7 Subway Line extension to the Hudson Yards and the Jacob Javits Center. Again, funding could become an issue here.

Not everything always goes smoothly with the major tunnelling projects - hardly surprising when it is considered that contractors are working at the limits of technology. On the Gotthard tunnel there have been problems on some sections where unexpectedly difficult ground have been met.

At Niagara Falls where Austrian contractor Strabag is driving the world's largest hard rock tunnel at 14.4 m diameter, unexpected ground conditions have slowed progress to a third of the speed originally anticipated. The alignment and gradient of the tunnel may be changed to try and keep the TBM in more suitable ground. Here the problem has been overbreak with weak rock conditions causing slow progress and lost time in cleaning up behind the machine. So far a little over 1.8 km has been driven of the 10 km long water diversion tunnel. Completion was originally scheduled for 2009, but could now be two years later than this.

Major sporting events seem to generate special tunnel projects. The Beijing Olympics have led to a big expansion of the Chinese capital's metro system, while on the west coast of Canada the 2010 Winter Olympics have been the prime mover in the Richmond-Airport-Vancouver (RAV) or Canada Line. This is a 19 km twin tunnel rapid transit link joining Richmond, Vancouver Airport and the Vancouver City Centre with a mixture of cut and cover tunnels, bridgework and bored tunnels being driven by a 6.1 m diameter Lovat machine. The most recent breakthrough was achieved in March this year.

In London, although not specifically an integral part of the Olympics construction programme for 2012, the recently completed Channel Tunnel Rail Link section from St Pancras to Stratford - the main Olympic site - will form a key part of the transportation infrastructure for the event. London's other major urban rail project, Crossrail, will not be part of the Olympics infrastructure. Although funding has now been approved completion will not be until after the Olympic Games.

Drill & blast

For many tunnelling projects, the choice between using a TBM and drill & blast can be pretty straightforward. Tunnel length and material are the key parameters when balancing the considerations of capital cost, tunnelling efficiency and diameter in medium-hard and hard rock conditions, where either technology can be used.

For shorter tunnels - and a huge number of road and rail tunnels around the world fall into this category, drill & blast is king. However, rock drill manufacturers would of course like their products to be chosen for longer and larger tunnels. To this end, huge strides have been made over the past few years in designing drill rigs, rock drills, feeds, drilling tools and computerised control systems to make their machinery competitive with TBMs over longer distances and greater cross sections.

Key in this area is the cross section that can be driven from a single drill rig. The latest rigs from the two major manufacturers in the sector, Atlas Copco and Sandvik, now being able to drill 180 m² + face areas from a single setup, putting them in competition with TBMs. Modern computer controlled drilling systems also enable them to drill longer rounds with more efficient breakage.

However, the continuous excavation provided by the TBM, coupled with smoother walls and the ability to line with concrete segments as the machine progresses does still give them the edge for many longer tunnels. Having said that drill & blast enables what can be a more suitably shaped tunnel to be driven, saving on excavation and muck removal costs.

Examples of the types of tunnel drilling rigs now available on the market - and these are being continually fine tuned to improve performance - are the Atlas Copco Boomer series of rigs and the new Sandvik DT Series (formerly known as the Tamrock Axera series).

The Atlas Copco Boomer rigs are a range of high-capacity drill rigs providing good overall economy, production capacity and well-proven reliability. The Boomer range can meet tunnel driving demands from 6 to 206 m² coverage area. The Atlas Copco boom system provides flexibility and an extensive range of rock drills 16 kW up to 30 kW impact power is available.

The company is currently upgrading many of its drill rigs and other equipment resulting in a range of improvements. In a project to upgrade its underground equipment with new diesel engines to meet the latest requirements in Europe (Stage IIIA) and North America (Tier 3), the company has redesigned and modified many of its face drilling and productions drilling rigs as well as bolting and scaling rigs.

Apart from the improved environmental impact provided by the new, lower emission engines, the design changes on the major part of the rigs have resulted in better hydraulic and automatic systems, increased safety and ergonomics, easier servicing and better reliability. Peter Öberg, who is managing the project at Atlas Copco's manufacturing facility in Örebro, Sweden said, "We have been able to increase the overall strength on several models which means that the rigs can carry heavier optional equipment. Due to new component layout and placement, serviceability and maintainability have been improved. This also enables the rigs to carry more optional equipment."

Most of the new installations and upgrades have already been incorporated into the company's assembly system and by June almost every new product will be built with the upgraded engine installation.

Sandvik tunnelling jumbos are built on tough diesel-driven carriers. They are electro-hydraulically powered and equipped with 2 to 4 booms, long feeds, fast hydraulic rock drills and advanced drilling control systems. With face coverage areas from 10 to 200 m2, all booms and feeds have automatic parallel holding with quick look-out auxiliaries for accurate hole placement, optimal profiling and minimal overbreak.

Some projects require a fair amount of drill and blast equipment. Among these is the 333.7 MW AHE Simplício hydro-electric power project in Brazil where five Sandvik underground jumbo drilling rigs, including a recently delivered, purpose-ordered Axera T11, are being used by a Brazilian joint venture. In total, construction by the Construtora Norberto Odebrecht and Construtora Andrade Gutierrez Joint Venture (JV), in a 36 month contract, incorporates eight channels, five reservoirs and four tunnels - including the longest at 6.03 km and featuring six working faces.

Throughout the tunnelling operations, the JV is relying on five Sandvik jumbo drilling rigs including a DT11 jumbo purpose-ordered by Construtora Andrade Gutierrez and two DT8s by Construtora Norberto Odebrecht. The fleet also includes a second DT11 and a DT8 on-rental to the JV; all featuring three booms and the Tamrock Computer Aided Drilling (TCAD) system (with the exception of the rental DT11).

The latest development of the DT rig is the i-series and in Finland, contractor Lemminkainen is using a new DT1130i on a multi-utility tunnel and underground excavation project with great success. Sandvik's i-series tunnelling jumbos feature several technical innovations which are claimed to make achieving good excavation quality easier than ever.

Scratching the surface

These are just a few of the tunnelling schemes currently underway around the world. IN addition, numerous new metros and metro extensions are being built in countries such as Spain, Russia, China, Italy, Iran, India, Portugal and more.

Road tunnels are under construction all around the world - notably where rough terrain necessitates much tunnelling. Norway, Taiwan and Portugal's Madeira (where there are 13 tunnels on a 19 km stretch of road between the airport and the city of Funchal typifying the engineering skills necessary on even a small island.) Other urban road schemes are under way in many parts of the world like Brisbane's North-South tunnel in Australia as cities battle to try and reduce congestion in their downtown areas. Hydro-electric schemes involving major tunnel systems are almost commonplace as the quest for renewable energy grows.

And, of course there is the largely unsung core tunnel business of wastewater handling which is the bread and butter of the sector, both in mature cities where existing networks are crumbling as well as in growing population centres where new infrastructure is needed. It is unlikely that tunnellers will go short of work in the foreseeable future. The problem may be whether there will be enough engineers and experienced engineers and tunnel crews to handle the amount of work available.