It is a given that muck handling and materials supply systems are key to the success of a tunnelling project. Often dictating the progress of advance as much as the excavation method itself, site logistics play a vital role in tunnelling, and can often make or break a project.
However, as the number of major projects in highly-urbanised areas increase worldwide, and the general public become more aware of the implications of adverse construction effects on environmentally sensitive rural areas, mucking and transport has taken on a much wider significance in modern day tunnelling.
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As such, the requirement to produce innovative, and often complex, logistical systems – to deal with factors such as limited site space, site access issues, multiple tunnel drives, conflicting infrastructure, traffic interfaces, and noise and environmental pollution – has risen to a new level.
City centre logistics
Often at the sharp end of public scrutiny are the high-profile high-budget projects that have the most potential to cause disruption. A number of the world’s largest cities are currently embarking on major tunnelling projects, where millions of tonnes of excavated material need to be removed, and supplies delivered, through highly congested areas. Each of these projects has its own specific challenges, often with extensive restrictions on vehicle movements and operating hours.
One such project is Phase 1 of the Second Avenue Subway, in New York, where to prevent local residents being disturbed at night, the movement of mucking and materials supply traffic through the streets of Manhattan is limited to the hours of 8am-10pm. The particular challenge of a night-time restriction on site traffic has entailed complex road diversions and careful planning of truck movements in New York’s congested daytime streets (T&TI, October, p29).
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By GlobalData“This is the opposite of my experience in Hong Kong,” says David Caiden, a principal of Arup, the design and construction manager on the project along with DMJM+Harris. “There muck and supply lorries could only be used at night, in order to avoid adverse impact upon the city’s traffic flow during the day.”
It is debatable whether overnight site traffic would actually have that much of an impact on Manhattan’s residents, considering the pre-existing background noise of the ‘city that never sleeps’. However, with numerous other tunnelling projects also shortly due to commence in Manhattan, the problem is likely to be cumulative.
Thankfully, the logistics of truck movements are not so much of an issue on New York’s East Side Access (ESA) rail scheme, which is currently being constructed by the Dragados/Judlau JV (p6). In contrast to Second Avenue, ESA’s Manhattan tunnel drives are being mucked almost entirely underground, utilising a combination of techniques within existing infrastructure.
Spoil is being transported, via conveyor, through the 63rd Street immersed tube tunnel, back to the Sunnyside railway yard in Queens (T&TNA, September 2006, p8). Rolling stock is also used, on the existing rail infrastructure, to supply the project’s two TBMs (segment cars, flat cars and mantrips) and also to muck the non-TBM driven excavations, such as cross passages.
“For me, this is an excellent example of rolling stock complementing conveyors,” says Bruce Matheson, vice president of business development for US equipment supplier, Mining Equipment.
Custom solutions
The key to determining the best project-specific solution for mucking operations is often a close working relationship with experienced equipment suppliers, the expertise of whom can be invaluable.
“The first question we always consider, is if our systems are the best option for the client,” says Pierre-Alain Scherwey, of Swiss conveyor manufacturer Marti Technik. “There are three main alternatives to consider – rail, tyre and conveyor systems. Most clients in industrialised countries know how to compare costs and the advantages of each alternative. However, by gaining a in-depth overview of a project, there is much we can do to assist clients in coming up with a global approach for their project.”
Michael Rowlinson, of solids separation specialist, Pigott Shaft Drilling (PSD), has a similar view. “We deal with each project on an individual basis. We speak to clients, ask detailed technical questions, review technical data such as borehole records, results from laboratory testing and undertake further in-house tests to determine which equipment may be the most suitable,” he explains. “We have personnel with expertise in, amongst other things, civil, geotechnical and mechanical engineering and pride ourselves in learning from projects and applying that knowledge to future projects and equipment.”
Matheson also believes staff experience and understanding client needs is key to Mining Equipment’s success as a supplier. “Our business is driven by efficiency, and sometimes conveyors are more efficient than muck wagons. The first thing we do is listen to clients and try to understand their requirements, then we can determine what we think will work best for them,” he says. “I do believe that the life-cycle cost of any conveyor should be taken in to account before the decision is made, including capital investment, resale value and the potentially dramatic effect a conveyor breakdown can have on production.”
Sometimes it is also a suppliers’ expertise that can enable the resolution of a specific problem. “For instance, on the Los Angeles Northeast Interceptor Sewer Project (NEIS), specific locomotive needs had to be addressed,” explains Brookville Equipment Corporation’s Michael White. “California’s OSHA declared the project one of the most hazardous tunnelling jobs in California, due to the discovery of methane and hydrogen sulfide gasses in the vicinity of the tunnel alignment. Brookville manufactured eight battery-powered, explosion-proof locomotives for contractor Traylor Brothers. By utilising a pneumatic system, along with Ansul fire suppression techniques, the locomotives were able to provide safe hauling operations in the dangerous conditions.”
“Our most recent challenge has been on a 5km long access tunnel for the Pajares 2 High Speed Railway, in Spain,” says Schöma’s Ralf-Peter Bogs. “There is an 6.3% downhill gradient, so the performance of the braking system is vital to the safety of the staff and the success of the transport system.”
“But problems not always technical,” says Matheson. “For example we are currently building new rolling stock for a project in Australia, which is going straight on to long-term rental. That sort of service is not offered by many in our industry.”
Minimising downtime
In terms of minimising downtime, manufacturers and suppliers seem to unanimously agree that the accurate specification of equipment, combined with robust designs and regular servicing provide the best result.
“Servicing is crucial, but luckily most of our customers fully appreciate this,” says Matheson. “Skilled contractors appreciate the value of maintenance; it reduces downtime, simple as that.”
“For any equipment, maintenance is a key point,” says Scherwey. “The TBM is the big machine and often the focus of all the attention. But, if the logistics don’t work well behind it, the best TBM in the world will come to a standstill. You can’t change the mucking system in the middle of a job, so it is essential to provide some contingency in the specification and undertake regular maintenance to prevent problems before they occur.”
Rowlinson also advocates a conservative approach to specification: “Clients often come to PSD having had poor experiences with their own in-house separation equipment or equipment from other suppliers. We design and build most of our own equipment and where possible over-specify equipment so that it does not have to work at its limit. It is absolutely critical, however, to allow time for routine maintenance. Some customers recognise this and reap the benefits, others do not and tend to suffer the consequences”
A good example of exactly how problematic the under-specification of solids separation equipment can be was apparent in last month’s news section (T&TI, October, p11). Just 20m into a 400m long TBM drive for the Pillans Point stormwater sewer, in New Zealand, tunnelling was called to a halt as a result of the centrifuges’ inability to cope with the volume of material being excavated. Larger replacement units are now being sourced, but the project’s completion will be delayed by months.
Multiple methods
Due to the sheer scale of some projects, the use of numerous transport methods will almost certainly be necessary.
This is the case for Brisbane’s North South Bypass Tunnel (p32), where enclosed conveyors will be used to transport material to a modern processing facility. Once processed, the material will be transferred to trucks fitted with GPS navigation to assist the navigation and timing of truck movements.
Having gained the green light from the UK’s Prime Minister last month, London’s US$32bn Crossrail scheme continues to look at a number of alternatives for removing the eight million cubic metres of surplus material that is expected to be generated during excavation of the project’s 41km of tunnels.
A spokesperson for the project told T&TI. “So far as reasonably practicable, the project has committed to limit adverse impacts upon local communities and the environment by transporting excavated material via rail and water.”
It is expected that the majority of the bored tunnelling operations will be mucked in this way, whereas spoil generated from the station caverns and shafts is likely to be removed by road.
Whatever the methods selected, it is certain that innovative logistics will be required to deal with the complex mucking transport and materials supply requirements of such a vast tunnelling project right in the heart of the City of London.
ESA’s combined use of conveyors and rail-bound plant, utilising the existing 63rd Street tunnel, enables minimal surface impact of the Manhattan tunnels ESA’s combined use of conveyors and rail-bound plant A spoil bunker on Sydney’s Cross City project – where existing infrastructure was employed to assist mucking operations A spoil bunker on Sydney’s Cross City project Trucks enter Sydney’s Cross City Tunnel via existing infrastructure, to pick up spoil from an underground bunker, before passing through a wheel wash on the way out A wheel wash within Sydney’s Cross City Tunnel Trucks enter Sydney’s Cross City Tunnel via existing infrastructure, to pick up spoil from an underground bunker, before passing through a wheel wash on the way out Trucks enter Sydney’s Cross City Tunnel An Algerian water tunnel mucked by Schoma rolling stock Two 9km long Marti conveyors handle spoil on Katzenberg’s twin bores, in Germany A 1350m3/hr PSD slurry treatment plant at work on the Kowloon Southern Link, in Hong Kong
