Deep Thinking: Shaft Design and Safety for a New Generation of Mines

Another factor at play over the past 40 years has been the increased use of mobile equipment at all stages of an underground operation, with access ramps having invari-ably been the preferred option over vertical shafts for equipment movement between surface and the stoping levels. When haul distances have got too long––as mines have become deeper—the production shaft has come into its own once again.

That is not to infer, of course, that no shafts have been sunk in the past 50 or 60 years—far from it—but the dominance of the big open pit in supplying major propor-tions of the world’s iron ore, copper, gold, coal and bauxite has pushed underground mining aside in many situations. Why, cor-porate finance officers would ask, go to the expense of developing a shaft and carry all of the cost implications of its operation when an open-pit will provide a better return?

This approach is still in evidence today, with recent examples having included the transition of Xstata’s MacArthur River base-metals mine in Australia’s Northern Territory from underground to open pit, and BHP Billiton’s current studies into a new, high-volume open-pit at its flagship copper and uranium producer, Olympic Dam. There is no escaping the reality that, until strip ratios become too high, surface min-ing has the financial edge.

Then again, one question that is becoming increasingly widely asked is: “What happens once the cost of running today’s open-pits gets too high?” There is nothing new about the transition from sur-face mining to underground: evidence of the practice can be seen from the locations of the earliest flint and metal mines all over the world. It is just that, for the past half-century at least, we have become accus-tomed to open-pit mining as being the way forward. And that, for an increasing num-ber of operations, looks set to change.

Today’s Design and Construction Expertise
Organized by the U.K.’s Institute of Materials, Minerals and Mining (IOM3 ), the Third International Conference on Shaft Design and Construction took place in London in late April. As the conference chairman, Alan Auld of shaft-design con-sultancy, the Alan Auld Group, noted in his introduction to the meeting, since the two previous conferences in the series took place in 1959 and 1989 respectively, it was perhaps timely to revisit the topic to provide an update on how concepts and technology have changed in the interven-ing years. Four of the speakers from the 1989 meeting had returned this time as presenters, he added, showing how shaft-sinking is a profession in its own right, and not just a mining offshoot.

The London meeting attracted around 175 delegates from nearly 20 countries, including the U.S., Canada, Australia, Germany, Poland and China, with no fewer than 40 papers presented over three days. Since civil engineering projects that involve shaft construction are much more common than deep mines in Europe, it was not surprising that a majority of the papers addressed issues associated with relatively shallow shafts, sunk in often challenging soft-rock situations.

Nonetheless, mine shafts featured prominently as well, with some excellent presentations provided on both design and construction aspects of modern deep-shaft development. In addition, the organizers accepted a couple of papers that, rather than looking specifically at shaft-sinking issues, reported on the overall develop-ment of China’s coal industry, in the con-text of the shaft-sinking requirements asso-ciated with some of the massive projects currently under way there.

Better by Design
Speaking from the perspective of one of the world’s leading shaft-sinking contractors, Roy Slack, president of Cementation Canada, looked at the design process for new mines and their shafts, and the impli-cations of any potential shortcomings there.

“Engineering is an integral part of the construction process,” he said, explaining that in any project, the greatest opportunity to make changes in a cost-effective way occurs early on in the time-line. “So much has to do with the upfront work, but it is often the case that the selection of a contractor only takes place halfway through the engineering design process.”

Making a forceful case for the early involvement of not only the shaft-sinking contractor, but also the hoist supplier and the headframe builder, he went on to state: “There are real opportunities to speed up a sinking project at the front end, when it is much easier to optimize procurement options by taking input from all of the par-ties involved.”

A sinking stage ready to be low-ered from the shaft collar (Photo courtesy of Shaft Sinkers)

The drill jumbo used at the Impala No.17 shaft. (Photo courtesy of Shaft Sinkers)

Procurement strategy is a critical part of the process, he said, adding: “Are we trying to build the mines of the future using the procurement practices of the past? If you are doing so, you are setting yourself up for a difficult project.”

With individual projects getting big-ger—and hence more costly—there has to be a symbiotic relationship between the mine owner and the shaft-development contractor that is driven by alignment and mutual trust. Making an analogy with nor-mal workplace practice, he pointed out that: “One of the key factors in a strong safety culture is the level of trust between the employee and his or her supervisor. Is there a similar relationship between the level of mutual trust between the mine owner and the contractor, and the ultimate success of a shaft-sinking project?”

Recent Shaft-sinking Projects
To put the topic into perspective, there have been a number of significant mine-shaft development projects undertaken in recent years, either for the development of new resources or where existing open-pits have become uneconomic.

One of the first major mines to have made the surface-to-underground transi-tion in recent years, the South African cop-per producer, Palabora, ended open-pit mining at the beginning of 2002. Since then, its ore has been won from a block-caving operation, serviced by a shaft, with the cost of developing the underground mine having been some $460 million at that time. Development included the sink-ing of production, ventilation and service shafts, as well as deepening an existing exploration shaft. In a paper presente

d at the SAIMM’s 2000 Mine Hoisting conference, J.J. Taljaard and J.D. Stephenson reported that “The production shaft is 1,290 m deep, 7.4 m in internal diameter and lined with 300-mm thick-concrete. The shaft is equipped with four [32 mt-capacity] skips operated in pairs by two 6.2-m-diameter tower-mounted Koepe winders. The pro-duction shaft has a concrete headgear, which accommodates the two Koepe winders.” Palabora also uses a 9.9-m-diameter service shaft, 1,272 m deep, that carries man/materials and Maryanne cages. Significantly in view of Roy Slack’s remarks at this year’s conference, these authors noted that the involvement of the contractor, Shaft Sinkers, “was deemed necessary to provide design input from a sinking consideration.”

While traditionally having been associ-ated with Southern Africa, Shaft Sinkers reports that it is actively seeking new mar-kets elsewhere in the world. Now with Kazakhstan-backed IMR as its main share-holder, the company’s first major interna-tional project has been at EuroChem’s Gremyachinskoye potash project in south-ern Russia, where it was contracted to sink one of the two main skip shafts. However, its chosen sinking method, involving pre-grouting unstable ground rather than freez-ing the whole shaft depth, proved to be incapable of handling the very poor condi-tions encountered, and Shaft Sinkers with-drew from the project in April.

Recovering from this setback—the grouting system having been targeted at saving EuroChem both time and costs over freezing—Shaft Sinkers announced in May that it had won a three-shaft sinking con-tract from Vedanta Resources for its Rampura Agucha zinc-lead mine, in the Indian state of Rajasthan. The project involves sinking a main production shaft and two ventilation shafts, and is sched-uled for completion in 2017.

Meanwhile, in South Africa, Shaft Sinkers has been working on a shaft-devel-opment contract for Royal Bafokeng Platinum at its Styldrift mine since 2010. This involves a 740-m-deep (2,425-ft), 10.5-m-diameter main shaft and a 705-m-deep, 6.5-m-diameter service shaft.

Other platinum-industry contracts for the company have included its work on Impala Platinum’s No.16 and No.17 shaft complexes, development of which began in 2004 and 2007 respectively.

Potash Projects Proceed Apace
One commodity that has received signifi-cant investment in new capacity, potash projects are now under development in all of the main centers around the world. In Canada, shaft-sinking is under way in both Saskatchewan and New Brunswick, while Russia’s potash-mining industry is also set for a major expansion. A new deep-mine potash project is even under evaluation in the U.K., and in each case, the arrival of new players into the market has under-pinned the surge in development activity.

In New Brunswick, Cementation has been involved with sinking the two new 890-m-deep, 5.5-m-diameter shafts for PotashCorp’s Picadilly project since 2008, with the company noting that the potential of water inflows means that the shafts have been designed and constructed with hydro-static liners.

Further west, Redpath group company AMC Mining is currently sinking a composite-lined shaft for PotashCorp’s Scissors Creek project at its Rocanville complex. The shaft development, reaching a depth of 1,123 m, has included 600 m of freez-ing as the shaft passes through the notori-ous Blairmore water-bearing formation, with AMC reporting that it designed an innovative headframe approach for the job that has led to the freezing circle being spanned by the permanent headframe, saving time and money since a sinking headframe has not been needed.

Other AMC projects in the province include its work on Mosaic’s K3 shafts— key to the company’s expansion of its Estahazy operation—currently involving the freezing contract. According to the project EPCM contractor, Hatch, the twin K3 shafts will be 1,127 m deep and 6.1 m in diameter, while the headframe will not only be one of the world’s tallest, but will house a Koepe winder capable of hoisting 54-mt-capacity skips.

Mid-last year, a joint venture between the German company, Siemag Tecberg, and the U.S. arm of Power Conversion (formerly Converteam), won the contract for the mine hoists and associated power-supply equip-ment as a turnkey package. Including both the 6-m-diameter, six-rope Koepe hoist and a 4-m-diameter Blair hoist, the equipment is scheduled for installation in late 2014.

Among the prominent shaft-sinking pro-jects undertaken by AMC’s parent company, Redpath, in recent years, top billing must surely go to its work at Oyu Tolgoi in Mongolia. It sank the first shaft there in 2006, and is now involved in upgrading it to its permanent production status. The sec-ond production shaft, now being sunk, is the largest it has ever handled, Redpath states, measuring 10 m in diameter by 1,320 m (4,035 ft) deep. The company will start sinking a vent shaft for the mine next year.

In January, Redpath further extended its capabilities in the international market with its acquisition of the German specialist, Deilmann-Haniel Shaft Sinking. Claiming a 120-year history, with more than 500 shafts completed, DHSS recently won contracts for two freeze shafts in the Urals region of Russia, as well as having current projects under way in Germany, Portugal and Bulgaria.

Installing a sinking stage. (Photo courtesy of Shaft Sinkers)

An Unusual Application
A paper presented to the London confer-ence by Dr. Joe Sopko and colleagues from the U.S.-based ground engineering firm, Moretrench American Corp., described a very unusual use of freezing technology— in this case, to recover ore remaining in a near-surface crown pillar.

Situated in the Rouyn-Noranda district of Québec, Noranda operated the Quémont mine from 1949 to 1971. On closure, some 11,000 m3 of zinc-bearing ore re-mained unmined at a depth of between 24 and 37 m (80-120 ft) below surface, over-lain by unconsolidated tailings and soft clay. Carried out by Layne Christensen (with whom Dr. Sopko was then associated) in 2002, the project involved creating a frozen wall in the overburden around the crown pil-lar location, with subsequent excavation of the ore by conventional drilling-and-blasting.

One key feature of the ice wall was that it had to provide structural strength as well as being water-tight. In consequence, the ice wall was designed 9.15 m (30 ft) thick, surrounding an excavation ‘shaft’ 61 m (200 ft) in diameter. Despite some early issues with freeze-pipe breakages, recovery of most of the ore was completed before a lightning strike knocked out the main freeze-plant power supply. In the words of the authors, “the construction of a large cofferdam using artificial ground freezing proved to be possibly the only successful method of retrieving the coveted ore.”

One of the great aspirations of mining and tunneling has long been the develop-ment of boring machines that can eco-nomically replace conventional drill-and-blast cycles. Rio Tinto’s focus on this, as part of its ‘Mine of the Future’ technology-development program, has already been well-publicized, with the German company, Herrenknecht, having introduced its SBS shaft-boring system in 2010.

At the London meeting, Herrenknecht’s Martin Rauer and Werner Burger described the subsequent development of the SBR shaft-boring roadheader concept, designed to ‘fill the gap’ between the large-diameter SBS system and the company’s VSM, which is designed for soft-rock conditions and is limited to around 100 m in its depth capa-bilities. The system, they said, is designed for drilling blind shafts up to 1,000 m deep in soft-to-medium ground, with the first of two machines scheduled for delivery in April to BHP Billiton’s Jansen project in Saskatchewan. Actual sinking is planned to start in September, with DMC Mining Services—now owned by Poland’s KGHM International—as the main contractor.

Rauer and Burger described the SBR as “a TBM turned on its head,” with the rotary cutting wheel used in the SBS replaced by a boom-mounted roadheader cutter. Pneumatic mucking removes the cuttings from the shaft bottom as they are created, with dust scrubbed from the ventilation air and a dust shield separating the cutting zone from the rest of the sinking stage. Five 200 mm-deep cuts are carried out before the entire machine is lowered by 1 m, with immediate sidewall support being installed while excavation is in progress.

Part of the ice wall created for the Quémont project. (Photo courtesy of Dr. Joe Sopko)

The Next Generation of Shafts
One thing made clear at the London meet-ing is the high level of technical input that is needed to meet modern shaft require-ments. As with most other aspects of hard-rock mining, the emphasis is on minimiz-ing personal exposure to potential hazards, with more sophisticated—and hence more expensive—equipment taking the place of the shaft-bottom drill crew with their pneu-matic sinkers.

Shafts will get deeper; of that there is no doubt, although ultra-depth shafts will require the development of lighter, stronger hoist ropes for them to remain economically viable. With conventional single-lift depth limits long having been reached, the potential rewards will have to be great indeed for those limits to be pushed further.

And, in some cases, those rewards may be immense. Take, for instance, the Resolution Copper project in Arizona, where Cementation is currently sinking a 2,130 m-deep (7,000-ft) exploration shaft. Or South Deep in South Africa, where the new main shaft is 2,995 m deep and extending the nearby ventilation shaft to the same depth is scheduled for completion this year by Murray & Roberts Cementation.

In Canada, meanwhile, Cementation reports that in recent years it has complet-ed two major shaft projects—the Kidd mine D No. 4 shaft and the Nickel Rim South twin shafts—without incurring a lost-time injury. Cementation’s contract for the internal, 7.62-m-diameter Kidd D No. 4 in-volved sinking 1,651 m to reach shaft bot-tom at 3,014 m below surface, while nor-mal mine operations continued above.

Whatever the scenario, wherever the project is in the world, shaft-sinking safety remains at the forefront of all the issues involved. “It’s a very competitive business, but there is a lot of collaboration between the competitors when it comes to safety,” Cementation’s Roy Slack told the London meeting.

Looking ahead, it is obvious that shaft design and construction expertise is going to be a very valuable commodity in its own right as mining companies dig deeper and deeper for the world’s commodity supplies. The costs of successful sinking may be high, but the costs of project failures will be even more.