Severe restrictions on the amount of space available on site, around portal areas and within shafts, is commonplace in today’s industry. Every job faces its own difficulties, but with a growing number of transport and utility projects in highly-urbanised areas – as well as the number of high-speed rail and hydroelectric projects being constructed in isolated or environmentally sensitive areas – organising the removal of muck from long, or multiple, tunnel drives can seem as much of an engineering challenge as the actual excavation itself. Increasingly, high-tech conveyor systems are able to offer practical and flexible solutions to many of these logistical issues.
Site solutions
“We have become quite creative in overcoming limitations in shaft or site space,” says Dean Workman, vice president of conveyor systems for Robbins. “In general, there are many options available for conveyor design and we are always able to work with specific site restrictions.”
For instance, on the East Side Access project, in New York, contracting JV Dragados/Judlau is mucking its Manhattan rock tunnel drives via a Robbins conveyor through the existing 63rd Street immersed tube tunnel, emerging at an open-cut box at the Sunnyside rail yard, in Queens (T&TNA, Dec 2007, p8).
In order to reach the temporary storage area, on the other side of the site, the conveyor has to rise up and traverse a four-lane highway, passing underneath the Northern Boulevard aerial rail corridor. “In order to achieve this, we designed a series of cascading conveyors, plus a completely-enclosed conveyor to cross the highway,” says Workman.
Vertical conveyors were also utilised on the UK’s Lower Lea Valley Cable Tunnels. One of the main logistical challenges here was the limited space available at the project’s central twin mining shafts (T&TI, June 2007, p18). With each of the 15m diameter shafts being used to muck and supply two separate Lovat EPBM headings, in highly-variable ground, the only way to safely manage crane operations in the shafts while also efficiently emptying the side tipping muck skips, was to adopt the use of High Angle Conveyors (HACs). Manufactured by Continental Conveyor, and supplied and serviced by Burrows Brothers, the HACs’ belts were fed from sumps incorporated into the base of each shaft during construction.
Contractor J Murphy & Sons has openly applauded the performance of the HACs, saying the extremely tight project schedule could not have been achieved without their use. There was a risk involved in the strategy adopted, as Murphy’s senior contracts manager Bob Brown admits: “There simply wasn’t a ‘Plan B’ if the HACs didn’t work out for us. It was a big decision, one that had to be taken very early on in the project. But under the same circumstances it’s definitely something I would do again.”
Pierre-Alain Scherwey, of Swiss-based manufacturer Marti Technik, agrees conveyors can offer very smart solutions when shaft space is tight, particularly for deeper shafts, but he also points out the additional benefits of using conveyors to move muck around or off a site: “Conveyors can free up a lot of space on the job site, allowing more room for construction traffic,” he says. “They can also transport muck long distances off-site for final disposal – negotiating roads, rivers and any other kind of obstruction.”
Such traversing techniques will be used in abundance on China’s Jinping II Hydro Electric Scheme, where Marti Technik subsidary, Marti-Xui Engineering, is currently constructing a huge conveying system on a steep valley side.
Marti-Xui’s contract includes the design, manufacture and assembly of over 6000 tonnes of steel structure to support the tunnel conveyors and main external conveyor. A number of suspension bridges and even a section of tunnel will also be required to negotiate the 7km journey to a processing facility further down the valley. The system has been designed to transport muck at a rate of 5000 tons/hour from five different tunnels, including three TBM drives and two drill & blast headings. At the same time, the return belt of the system will bring concrete aggregates back up from the processing plant to the concrete plant.
Following commissioning of the system, this summer, a total of more than 25,000,000 tons of muck and aggregates are due to be transported on the system.
New lengths in India
Longer conveyor systems are indeed becoming increasingly common features. “There has been quite a lot of interest in using belt conveyors for overland transportation recently,” says Workman. “The cost of using trucks to move spoil has gone up dramatically, both for petroleum-based tires and the large amounts of fuel that such vehicles require.” Conveyors offer cost savings in this respect, and have the added environmental benefit of using electric motors rather than diesel.
A recent Robbins conveyor design, made for the Pula Subbaiah Veligonda Tunnel #2 in India, tops out at 19.2km in a single conveyor flight. The contract, awarded by Coastal Projects Pvt, also includes the supply of a 10m diameter Double Shield TBM and back-up system.
The water tunnel will follow a straight path through quartzite, shale and phyllite and will travel underneath India’s largest tiger sanctuary – the Nagarjunasagar Reserve. Both the tunnel length and environmental concerns including excess noise and exhaust meant that conveyors were the only feasible option for muck removal.
“Conveyors are the most non-invasive method compared to locomotives and muck cars, which are often noisy and emit exhaust during operation. The trains also require more maintenance and are less efficient on longer tunnels, where they must keep up with the excavation rates of high-powered TBMs,” says Workman.
As a result, long tunnel projects using continuous conveyor systems rather than muck cars often experience higher rates of system availability. For example, the Epping to Chatswood Rail Link tunnels in Sydney, Australia, achieved an average rate of 94% system availability with continuous conveyors, despite the extensive tunnel lengths and more than 80% of the bore path being curved.
The design of the Veligonda conveyor system is also tailored for maximum efficiency. The system, consisting of the longest conveyor drive Robbins has ever provided, will allow maintenance and belt splicing to be performed outside of the tunnel in an optimal environment. To take the belt to greater lengths, more powerful drives are needed as well.
The steel cable belt system will be powered by a total of seven drive motors – one main drive with two 300kW motors at the tunnel portal plus three booster drives with a total of five motors inside the tunnel.
“In theory, we can make still longer conveyor systems, though this will depend on the tunnel alignment and the expected capacity of the conveyor system,” explains Workman.
Conveyor components at Veligonda can be interchanged with those of its sister tunnel, the AMR Project, contracted to Jaiprakash Associates by the Andhra Pradesh government. The tunnel sites are two to three hours away by road and will utilise nearly identical conveyor systems, making exchange of belt rolls and other parts relatively easy. The scheme is part of Robbins’ goal to create universal components for as many conveyor systems as possible, though this is necessarily limited by variables including belt width and tunnel alignment.
Variables in each conveyor system are determined by the contractual penetration rate of the TBM – a higher penetration rate will require a wider conveyor belt to handle more muck, for example. Excavation rates established depending on rock type, rock hardness, machine type, and a host of other factors. The AMR and Veligonda Projects will utilise nearly identical Robbins TBMs and will bore through similar rock, resulting in the same expected penetration rates and interchangeable conveyor systems using 914mm wide belt.
“The design of these conveyor systems looks to be simple and user friendly, though the efficiency still needs to be tested as the projects start up,” said Anil Kamat, project manager for Jaiprakash at the AMR jobsite. Once complete, both Veligonda and AMR Projects will become part of a larger system to draw floodwaters from the Krishna River for irrigation and drinking water. The water will be distributed through a network of canals to over 400,000 acres of farmland and villages in the arid state of Andhra Pradesh.
Keeping Katzenberg clean
The new 9.4km long twin-tube Katzenberg Tunnel forms a central element of the current Rhine Valley Railway upgrade between Karlsruhe, in Germany, and Basel, in Switzerland. Already a key route for national and international rail traffic, once upgraded the line will also provide access to the Alpine rail routes (NEAT) currently being built in Switzerland.
A JV of Ed Züblin, Wayss & Freytag, Marti Tunnelbau and Jäger Bau completed excavation of the 9385m twin-tube tunnel in October last year, using two 11.12m diameter Herrenknecht EPBMs. Launching the first machine on the East tube in May 2005, and the second on the West tube in the September, the Katzenberg TBMs drove north through the region’s limestone, sandstone and marls, at depths of up to 110m (T&TI, November 2007, p7).
The strategy for disposal of excavated spoil from the twin parallel tubes, and the selection of a suitable system for charging the final disposal site, placed big demands on the project in the planning phase. A particular challenge was that excavated material could only be transported to the final disposal site, 2.5km away at the ‘Kapf’ quarry, during restricted time periods. This meant that an environmentally-sensitive temporary muck holding site would also be required on site.
In collaboration with the JV, Marti Technik designed, manufactured and assembled a complex mucking concept, that focused on operational reliability and ease of maintenance. “We design all our conveyor systems with the help of software that enables us to simulate any scenario on-screen. This allows us to determine the most appropriate components and system features for each element of the conveyor.”
Thanks to a near straight tunnel alignment, Katzenberg’s two 9km long continuous conveyors could operate the full tunnel distance with a single-pull system, powered by head units at the portals – avoiding the need for additional boosters. This greatly reduced servicing and maintenance requirements in the tunnel.
The conveyor also included a high-performance control command system, that can collect data from numerous sensors and transform it into information that can be used to improve performance.
“The sensors detect hopper or belt overloading, return drum rotation defaults and even whether or not the conveyor structure is assembled correctly for the next TBM advance,” explains Scherwey. “Everything, including video monitoring, is visible via control screens in the TBM cabin and in the control centre on the surface. This helps the contractor to improve on performance and site organisation.”
Safety of tunnel personnel was also considered during the conveyor design. “We design all access, working and maintenance areas with safety in mind,” says Scherwey. Walkways are all anti-slip, with handrails, and steps and stairs are used instead of ladders. There are also grills over all the rotating parts and extra room is provided around the belt scrapers for maintenance. Emergency stop buttons, lockout systems, warning lamps and sirens are also located at regular strategic points along the conveyor.
Into the future
The technology, reliability, safety and cost of conveyors has much improved over recent years, with key suppliers plowing a huge amount of accumulated project experience back into their design and production processes. Higher quality components, due to tighter manufacturing tolerances, play a big part in increased performance. “What determines the power and efficiency in a given system is how much friction is present,” says Dean Workman. “Better components take less resistance to run and use less energy, which means longer lasting systems.” Workman also credits variable frequency drives with Programmable Logic Controllers (PLCs) as another recent improvement, as they control the output torque: “In very long, multi-drive conveyors systems with booster drives, for example, the PLC can balance loads on each drive to maximise efficiency.”
The costs of conveyors are also being reduced by manufacturer’s efforts to standardise components and simplify system designs. Refurbishment of existing systems, and bespoke rental systems fitted with refurbished second-hand components, are also a key revenue streams for conveyor manufacturers and suppliers.
“On rentals, we guarantee machine availability, provide and guarantee wear and spare parts, splicing tools and materials, and also provide on-site training,” says Scherwey. “Ultimately, we want to provide a very interesting global cost, along with reliability and performance.”
In terms of possible future developments, Dean Workman believes there are two main areas that will soon impact: Even more advanced electronic controls; and new developments with conveyor belting.
“For controls, there will be better monitoring of the entire system. This is already happening to some extent – on East Side Access data is recorded on a laptop in New York, which we can access from our office in West Virginia. We can view the entire system, making troubleshooting easier.
For belts, new designs will include embedded computer chips to provide additional monitoring. Data including when the belt was installed and how many times it has cycled through the system can be used for maintenance. Currently engineers are still working on developing a computer chip that can withstand the heat and pressure of the belt manufacturing process, but once this is achieved we will know much more about the systems at any given time.”
The vertical and enclosed-horizontal conveyor set-up for the East Side Access project Continental’s HACs in use on the UK’s Lower Lea Valley Cable Tunnels HAC conveyor sump at the base of one of the Lower Lea Valley Cable Tunnel shafts, in the UK A Marti Technik bucket belt for vertical conveying Detail of a Marti Technik hopper and conveyor set-up, as used in Melbourne, Australia Long-distance off-site conveyor transport, by Marti Technik A Marti Technik covered suspension bridge conveyor spans a river Marti’s high-performance control command system AMR’s Robbins conveyor system shares common components with Veligonda’s Katzenberg’s temporary muck storage area Katzenberg’s portal area, showing the installation of the Marti Technik conveyor system A Marti Technik compact belt cassette sits just inside a tunnel portal
