Whether they be short or long, deeper or steeper, the tunnelling challenges on many projects are often pushing new limits to achieve necessary solutions in mucking out, and adding ever more choices.
As Bruce Matheson, sales and marketing director at Terratec, observes, "Like everything underground, there can be no blanket solution – everything is case by case, and it is dependent on the project, time scale, budget and, of course, the equipment the contractor happens to have."
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Tunnels’ brief sampling of projects – excluding slurry pumping – has shown varied combinations of wheels, rails and conveyors in play. In addition, there is more new loading kit to choose from.
As Matheson comments, "The market is a bit confused out there, choices are made that you would not think of first off – but in the end they work out great – it’s all about thinking outside the box."
Belts and EPBM
While it has a growing range of excavation equipment, Terratec’s journey in spoil removal is focused on continuous conveyor system, and includes its own design of a floating tail piece, patented almost 22 years ago and used then as part of the tunnelling package for the Prospect Reservoir scheme, in Australia.
For other projects, the firm has provided different solutions from trailing bunker conveyors to overland conveyor transfer systems. Terratec, he says, prefers to use a solid woven belt as its ‘belt of choice’, a product connected with their origins deep in the Australian mining industry, and built on that sector’s generations of muck transport experience.
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By GlobalDataMatheson says, "The beauty of it is the increased tension it can take, and on top of that, as it’s a matrix weave structure, it is basically rip proof."
Projects recently supplied with Terratec conveyors as part of tunnelling packages of various sizes, include works on two metro schemes: Line 2 in Santo Domingo, which also called for a refurbished 9.56m diameter EPBM; and, most recently, Bangkok metro’s Blue Line Extension project which called for a 3.2km long belt system along with a 6.44m dia EPBM – and both having to be capable of a 160m radius curve.
He says that one of the interesting aspects of the Blue Line system is that the belt feeds skips on a car passer in the shaft. The skips are lifted out and dumped or can be stockpiled in what is a very congested site in downtown Bangkok. The contractor is Italian-Thai Development.
"This saved the contractor the expense of a vertical conveyor and allowed them to use existing equipment," he says. "It’s all about being flexible and that’s something we pride ourselves in."
Another TBM and continuous conveyor package, this time from Robbins, is currently excavating on quite a different project – opening up two decline tunnels at Anglo American’s Grosvenor coal mine, in Queensland, Australia. The machine is a hybrid single shield/EPBM, and the tunnelling system is operating on steep grades – 1:6 and 1:8, respectively – through mixed ground conditions, though mostly sedimentary hard rock is anticipated.
Robbins notes that continuous conveyors have been ‘tried and tested’ with hard rock TBMs for decades, but there is a surge in growth with soft ground shields. It comments that efficiency advances coming from electric variable frequency drives could give conveyors ‘potential to corner the market’ for mucking out behind EPBMs.
The ability of belt wipers and scrapers to ‘deal with wet, sticky material as well as hard rock,’ means, says Robbins, that while projects have variable geology, ‘ground conditions have little bearing on conveyor operation.’
Steep and Long
Another project where the drives are steep and the tunnels long, and is using a conveyor solution for mucking out, is the tunnelling on the east end of the Ryfast project, near Stavanger, in Norway. However, here the rock is hard and, unusually in working with long conveyors, the excavation method is drill and blast.
Contractor Marti is blasting the twin tunnels through gneiss and opted for the spoil removal solution as it is building part of what will be the world’s longest subsea road tunnel scheme. Over less than 8km, and after a relatively shallow start from the Solbakk portal, the contractor’s section of the Ryfylke tunnel – the longer of the two in the Ryfast scheme – will reach 230m below sea level at its lowest point, having descended mostly at a grade of seven per cent.
Sandvik, which has supplied the jumbos to the Solbakk works, observes that Marti has been able to draw upon its TBM experience to conceive of adopting an extensible conveyor system for mucking out.
The spoil is taken a few hundred metres back from the face by wheel loaders, which tip the rock into a feeder-breaker system before the crushed rock is passed on to the conveyor, and discharged beyond the portal.
The manufacturer adds that the conveyor solution should help improve safety as it will help to minimise vehicle movements in the tunnels. It observes, too, that "running fully loaded dump trucks for long distances up such a slope would be extremely demanding on the equipment."
With long tunnels presenting major challenges for mucking out, another instance of such a project is the Alimineti Madhava Reddy (AMR) water tunnel, in India. At 43.5km long when finished, it will be the world’s longest tunnel built without intermediate access.
One of the two Robbins TBMs on the project met problems when fractured rock damaged both the shield and conveyor belt, requiring both repairs to be made and deflector plates added at the cutterhead chute. But, even apart from those difficulties, the task of operating and maintaining such a long continuous conveyor system is "a challenge in itself," says Jim Clark, the manufacturer’s country manager.
Deep
Another long tunnel is the Emisor Oriente wastewater scheme, in Mexico City, which is being bored by six TBMs – split evenly between Herrenknecht and Robbins. While length is one of the hurdles for mucking out, the other excavation challenge does not arise from steep grades because it is a hydraulic tunnel but, instead, comes from its general depth – the shafts range in depth from 50 to 150m.
The 62km long tunnel system has had to located deep underground as a key part of the major drainage solution to the capital and its suburbs. The challenge for tunnellers, then, is mucking out from the deep shafts on the project, and a sites in varied situations.
Supplier H+E Logistik describes its 5.3km long conveyor with 500m horizontal belt storage capacity supporting one of the three Herrenknecht EPBMs on the project; the manufacturer provided two 8.7m shields and a 8.9m machine. H+E is part of the same group.
On the project, Robbins has used J-type vertical conveyors and vertical belt cassettes supporting its trio of 8.9m diameter EPBMs. One vertical cassette is 34m high, allowing for extension and splicing of the belt on a small footprint at tight shaft site.
Heights of vertical conveyor systems have been growing to meet, and overcome, similar large lift challenges in the recent spate of deep tunnels. On the Mumbai Water Tunnel IV project, the vertical conveyor raised muck 122m up the shaft. Behind the 6.25m dia Herrenknecht shield, the entire H+E conveyor was 6.8km long with 500m horizontal belt storage capacity.
"For vertical conveyors of that life height it is always a challenge for installation of the pocket belt itself," says Martin Koch, senior project manager with H+E. He adds, "As the belts have a high weight per meter, and has to be lowered into the shaft from the top.
Depending on the site and available space, it is done by special machinery to lower the belt step by step."
Shifting Challenge
Sometimes, though, more complicated circumstances arise in and around water tunnels, such as the varied vertical alignment at Ontario Power Generation’s Niagara Power Tunnel, and the surface waterways that needed to be crossed by the mucking out system – again, a conveyor and TBM solution.
A large diameter bore, the tunnel was commissioned last year and now conveys extra water to boost generation at OPG’s Sir Adam Beck power plant. It is a little over 10km long but the original design featured grades of more than seven per cent at each end.
During excavation, the overall result was a net lift of 40m, but the slopes and also horizontal radii led to changes in tension along the length of the conveyor. H+E supplied the conveyor.
During construction, geological problems for the TBM bore led to a redesign of the tunnel’s vertical alignment, and introduced yet more grades.
In part, the re-design of the mucking system involved relocating the booster drive.
Once the spoil from the 14.4m diameter Robbins machine was up on the surface, the challenge at Niagara was not over. The conveyor transfer system had to get over the wide waterways, and a large single-span bridge had to be installed using cranes.
Contractor Strabag pulled back months from the revised programme deadline, and at less cost, which enabled the client to start generating extra electricity and earning more revenue sooner than had been anticipated when the tunnel was suffering overbreak during excavation.
Not up, but away
While the Niagara setting offered tunnellers uncongested, open space to arrange the surface portion of their conveyor system, no such luxury is afforded in urban environment, especially in the likes of New York.
On the East Side Access (ESA) project, being developed by the city’s Metropolitan Transportation Authority (MTA), the challenge was how to muck out from caverns being blasted out not below the expensive real estate of Manhattan. The challenge was a bit trickier still: the caverns are below the existing, low-level ‘Train Shed’ where commuters already embark and disembark before going upstairs – to the concourse of the world-famous landmark, and cathedral-like space, of Grand Central Station.
No way to get up and out, of course. However, as with many long tunnels, the answer to removing spoil from the massive cavern excavations was to take it out the way the plant got in. In the case of ESA, a series of hard rock TBM drives had bored their way below parts of Manhattan, and the tunnels would form the main link in the future commuter extension of the Long Island Rail Road (LIRR).
As the caverns would house the future LIRR terminal below Grand Central, the TBMs came all the way into, and beyond, the station zone, carving out much of the voids in repeated jabs. And then they were gone, retracted, and dismantled. When the underground works contractor Dragados/Judlau JV then moved to blast out from the stacked bores, taking out headings, pillars and benches, they elected to cavern spaces to muck out when a combination of wheeled loaders and rail wagons.
The spoil trains would then shuttle out along the bored tunnels, snaking off towards Queens to emerge at the surface.
The excavation and mucking task completed, construction has moved on to cavern waterproofing and lining, and ESA is looking at an in-service target date of 2020.
Loading answers
Sandvik and Atlas Copco have new offerings in loading for the tunnelling market.
Sandvik
Sandvik introduced the lh204 loader to the mining sector in April, and the product would be equally applicable for tunnel projects, says Tomi Pikala, marketing manager for loaders.
"it’s designed for underground mines but nothing prevents you to use it in tunnelling or even open pit," says Pikala. he adds, "it is possible and a very handy tool also for tunnelling projects, but some bigger models like lh307 and lh410 are more common due to physical size and capacity."
While the lh204 can work well in a 3m by 3m tunnel section, it is capable of operating within a tighter space, such as 2.5m by 2.5m, says Pikala. it was designed for supporting the mining of narrow-vein ore bodies, and has a 4 tonne capacity.
"Minimum tunnel size depends on local regulations," he notes.
The new feature in the size class is locating the operator in the rear frame away from spilling rocks. "this improves safety quite a lot," says Pikala. The loader also has an onboard diagnostics tool, uncommon to the size class, he adds.
In discussing operating in tight spaces, he also points to ‘some interesting existing technologies’ – side-tipping buckets, and ejector buckets with push plates to speed up the discharge process.
Atlas Copco
While Atlas Copco has further filled out its loader range with the introduction of the 18 tonne capacity scooptram st18 loader, for long and tighter mines and tunnels the company has on offer the Haggloader for continuous loading.
Atlas Copco launched the Scooptram st18 at the end of last year. In the announcement, product manager Ben Thompson said the ‘long-awaited’ loader had an optimised bucket, meaning "better muck pile penetration, faster acceleration and faster dumping."
He added: "the result is a better load factor on the truck and, in the end, a higher tonnage per month."
The Haggloader is available in different sizes as well as mountings – on wheels (7hr & 10hr models), rails (8hr) or crawler tracks (9hr). Fully capable of loading itself, the haggloader can be equipped either with digging arms or a back-hoe system to load the conveyor. Tunnel drift areas for the models are minimum 8m2, except for 10hr which is minimum 14m2.
Atlas Copco says the new system is a system-match with several of its haulage vehicles, such as the 10hr model working with the minetruck mt42. In addition, the Haggloaders can work with its HaggCon shuttlecars, adds the manufacturer. The wagons have four capacities from 6m3 to 14m3.
