Developing a blueprint for TBM mine access 16 Oct 2014

To date there is only one other example of a TBM being utilised in Australia for excavation of a surface-to-seam access tunnel – the West Cliff Mine drive in New South Wales in the 1970s. However, the lining on that project featured a standard rockbolt/mesh/shotcrete configuration, making the Grosvenor Mine tunnel drives – the first of which was completed successfully last month – a potentially important first for the integration of TBM and segmental lining techniques.

There are those in the civil tunnelling construction and TBM manufacturing industries who believe that now - more than ever before - the mining industry may be ready to reevaluate old principles and look seriously at full face excavation solutions. Which is why well-respected Australian civil tunnelling contractor McConnell Dowell has invested heavily over the last two years developing a “one-size-fits-all” design solution, not only for the excavation of drift access surface-to-seam tunnels, in-seam tunnels and vertical shafts, but also for ventilation and tunnel lining as part of an overall design package. A kind of “off-the-peg” civil tunnelling solution that offers two attractive benefits: the potential to open up mine production three times faster than roadheader excavations, and longer design-life tunnels that are safer and less expensive to maintain.

8m Robbins EPBM for Grosvenor Mine access

One of the major obstacles in the way of consistent application of TBM technology for mine access is, quite simply, cost. At US$15-30 million for a new TBM, the unit price for excavating what might often be just 1,000-2,000m of heading is all-too-frequently regarded as prohibitive. McConnell Dowell, of course, is aware of this, but believes that by investing in a small number of standardised blueprint designs, and TBMs/VSMs that are bespoke to the specific needs of the coal mining industry, it can cut operating costs dramatically. Its business model, drawn up in joint venture with leading Australian coal mining contractor Mastermyne (who together form MDMJV) removes the client’s project risk of having to assume full TBM cost for what are potentially short drives. By retaining the machinery to deliver future mine projects for future mine-owning clients, the MDMJV also assumes responsibility for post-project storage, transportation and disposal logistics.

MDMJV has appointed leading German TBM manufacturer Herrenknecht as preferred supplier for a machine that will be capable of delivering full face excavation of in-seam (IS) tunnels and roadways – a long-term market which, according to McConnell Dowell (MD) tunnel manager David Sibthorpe, who heads the MDMJV, has “huge potential for hundreds of kilometres a year.” In the nearer term the JV is collaborating with a number of suppliers for design of the surface-to-seam (S2S) drift access TBM, which Sibthorpe believes has a potential annual market of “thousands of metres per year.” Broadly speaking it will be a modified 8m diameter rock TBM.

Flat invert TBM for in-seam excavation

“MDMJV have appointed Herrenknecht as preferred machine supplier for the in-seam machine only,” Sibthorpe told TunnelTalk from Australia. “The effort they made in providing engineering solutions to our preference for a machine capable of delivering a flat invert made this a logical move. The surface-to-seam machine development is ongoing with a few suppliers.”

He added: “We have developed what we believe to be the optimum tunnel diameter, a lining configuration that incorporates a hexagonal segment system for rapid advance, and a machine specification that will suit most applications. We propose that delivery in a single pass, inclusive of the ventilated invert and flat roadway, is the best outcome for construction and future use of the drifts. Detailed review will be required of each application, however we are proposing a boiler-plate solution that fits within certain parameters, and will deliver repeatable results.”

“We have researched what drift dimensions have been nominated over recent history, dating back more than 15 years, and developed a configuration that provides a clear opening above the roadway surface of 7m x 4m. This is large enough for current, and likely future, longwall components, and fits neatly within an 8m lined drive.”

Mindful of the fact that future contracts are likely to include vertical shaft excavation MDMJV has engaged Herrenknecht, and another supplier, to develop to its own specification a suitable VSM solution. “There are two markets for this, one being the New South Wales market that currently wants 6m lined shafts unto 350m in depth, and the second is a Queensland version to cater for demand there for shafts of smaller diameter, around 4m, and to a much shallower depth of 200m only. Both these two systems are being developed.”

Flat invert TBM tunnel profile

McConnell Dowell has been proposing TBM access for coal drifts for nearly 10 years now, and tendering for jobs on that basis – but with little success. “Lots of companies were interested, but everyone wanted to be second,” said Sibthorpe. “We tendered a few TBM only drifts, none of which proceeded. It is our understanding that the Grosvenor drift was awarded on an alternative and originally tendered as a conventional drift also.” Now that a first step towards acceptance of TBM methodology has been taken by Anglo American in Queensland, the MDMJV is hoping it has positioned itself well over the last few years to take advantage.

Sibthorpe said: “We aligned with Mastermyne on a conventional drift tender because I knew them by reputation. I could see that McConnell Dowell needed the sector credibility to secure work. We were seen by mine owners as the alternative, perhaps one to consider if the standard players were too busy, too small, or the job was too specialised. By joining with Mastermyne we became not just a standard player, with the credibility and culture; we became arguably the most robust player – with the McConnell $3bn turnover and TBM experience, combined with the Mastermyne coal reputation and track record.”

“If you were a mine owner looking to contract out 500m of in-seam driveage there are probably a handful of Australian contractors to speak with; if you were looking to contract out 20,000m of in-seam driveage then Mastermyne stand alone. The have the in-seam contract market reputation for safe delivery, they have the training facilities, they have a services division that provides engineering and equipment, and they have the contacts. They open doors at the right level.

Vertical shaft excavation and lining

“Once we started tendering together we realised that the Tunnelling & Underground Business Unit of McConnell and Mastermyne were not so different, except for the fact our core businesses were different sectors. The management culture, the way we interact and communicate, and the way we respond to client requests and questions is very similar. It has been a great fit, and although untested on site to date I am very confident that it would continue to operate as it does now.”

At this stage the venture is for Australia only, but Sibthorpe believes that TBM access projects will be financially viable, especially in countries where labour costs are high. “At this stage this venture is Australian only, until at least we develop a track record and can demonstrate efficiency and repeatability, then overseas markets can be investigated. The reason the Australian market is right for this is that the labour component on a drift project can be as high as 60% of project cost, so if you deliver them faster and with less manpower they are more efficient.”

Overcoming mining industry antipathy towards civil tunnelling techniques remains a big challenge, but the long design life of segmentally lined tunnels is becoming a more attractive option for mine owners. “Convention remains to bolt/mesh/spray a drift knowing that periodically, say every 10 years, large sections will require remediation works. Anglo American had a catastrophic failure some years back that closed their mine for months, hence the Grosvenor zero-risk approach. We are asking mine owners to look at OPEX savings over the life of a mine in demonstration of value in spending CAPEX today; basically money is cheaper now than it will be in 10 or 20 years time. In this way a segmental lining, while more expensive, is actually better value.”

McConnell Dowell, Mastermyne and Sibthorpe may soon be rewarded for their years of work developing a blueprint for an “off-the-peg” civil tunnelling solution for the mining industry. Following breakthrough on the first of the two TBM excavated drift tunnels at Grosvenor Mine, Anglo American Underground Construction Manager Adam Foulstone conceded that civil tunnelling was the “better methodology,” adding: “Use of TBMs opens up a new chapter not just with Anglo American, but with the whole coal industry in Australia. Now we can draw up a new coal mine in less than a year, compared with two to three years if we use roadheaders. Anywhere we need to get men and materials into an underground environment is an opportunity to use a TBM”.

McConnell Dowell is confident that teaming up with Mastermyne will increase its ability to break open the mining industry to civil tunnelling techniques, but Sibthorpe realises there is a hard sell ahead. “Once this method becomes the default, which i am confident it will, then mine planning and costing will include this technology, and then first coal will no longer be two or three years from site access, it could be less than one. The potential for the civil tunnelling industry is huge, but the challenges for us are great also, not least of which is the mindset within the mining industry that what is done now is acceptable and dependable.”