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Founded in 1990, Tulloch Engineering is a Canadian firm with about 200 employees and eight branch offices in Ontario. There’s a lot of mining in this part of the world, and providing surveying and engineering services to mining multinationals like Vale (the world’s 2nd largest mining company) and Xstrata is an important component of Tulloch’s business strategy. So the company strives for efficiency in mining services, and is always looking for ways to use new survey technology in mining applications.
This progressive attitude was recently honored by the Association of Canada Lands Surveyors (ALCS), the national licensing body for Canadian surveying professionals. The association awarded its annual David Thompson award for Innovation in Geomatics to a Tulloch team for "Innovation in Geomatics." Specifically, the team was honored for applying terrestrial LiDAR scanning to mining work, and the honors are deserved; Tulloch crews have been taking a Leica Geosystems laser scanner below the surface, sometimes 8,000 feet underground, and finding ways to maximize the efficiency of mine surveying.
It should also be noted that Tulloch Engineering won a second David Thompson award in 2013, for "Unusual Applications in Geomatics." This award was for scanning work done on a newly refurbished runway at Ottawa International Airport.
Taking LiDAR undergroundway underground
We work mainly in nickel and copper mines, and those mines also produce some gold and platinum, explains Tulloch Party Chief Luc Battison. My crew does most of the underground survey and scanning work on mine sites. We do layout for new shoring and structures, establish line and grade for drifts, and whatever else is needed. We try to be a versatile crew and fill in wherever were needed.
This type of mining takes place deep underground, from 3,000 feet to as much as 8,000 feet below the surface, and comes with its own special set of problems. Compasses, for example, dont work at all, and surveyors sometimes use gyro meters to establish azimuths. Laser scanning is no different. Scanning in mines has several unique features, compared to above-ground mining, and the differences are instructive.
Conventional surveyors typically think of their work in terms of planes, or surfaceseven a complex topographic survey is reducible to one surface, topologically, and it can usually be adequately represented on a 2D surface, either paper or a screen. Put another way, most surveyors are rarely inside the thing they are surveying.
But mine surveyors are always inside their work. Moreover, they are nearly always concerned with volumes, not surfaces. Accurately measuring the drifts (horizontal or near horizontal openings or tunnels), stopes (caverns created when removing ore), raises (vertical or inclined excavations leading from one drift to another), adits (horizontal mine entrances), and access corridors is absolutely crucialmining engineers need this information to design suitable shoring structures, to install ore removal systems and, generally, to operate the mine safely and efficiently.
For example, in one of its Ontario mines, Vale recently started using electric trucks made by Kiruna that were larger than previous trucks, and this necessitated a great deal of excavation to adapt critical mine passages to the new, larger vehicles. So, these passages needed detailed volume surveys in order to make the necessary excavations and only the necessary excavations. Mining operators obviously dont mind removing rock when needed, but they also dont want to waste effortand they also dont want to remove rock that might be preventing collapses. Good surveys, in three dimensions, helped them to plan out minimum necessary interventions that are safe and efficient.
Tulloch crews used to do this work mainly with a combination of reflectorless total stations and photogrammetric imaging. But in 2012, Tulloch became the first survey contractors in Ontarios Sudbury Basin (Earths second largest impact crater) to use terrestrial laser scanning in mines. The firm bought a Leica HDS7000 high-speed laser scannerWe liked the HDS7000 because it had the resolution, power, and speed we needed, and because it was well sealed; fine rock dust is a major problem underground," says Battison–and set about learning how to do LiDAR scanning in mines.
Go here to learn more about long-range scanners for mines or visit www.leica-geosystems.us.
The advantages were immediately obvious; LiDAR scanning enables precise collection of data at a much faster rate than conventional underground total station survey methods. The Leica HDS7000, for example, captures a million observations per second with a relative error of less than a millimeter. Moreover, the point clouds created by scanning lend themselves very well to the creation of various 3D representations, like digital wireframes or series, or vertical or horizontal `slices,’ that are immediately useful to mine operators. Tulloch designers use Leica’s Cyclone software to edit and process point clouds, and then export the clouds to Technodigit’s 3DReshaper to create various 3D surfaces and representations.
Compared to total station work, every aspect of this is revolutionary–basically, the feeling at Tulloch is that there’s no going back.
But the enormous potential of laser scanning in mines didn’t mean there weren’t problems to overcome. Just getting oriented is a little trickier in mines. In order to integrate scan data into mine site coordinates, control points have to be installed in the mine’s various caverns. A gyro meter is used to control the azimuth of the mine site coordinates, and precise leveling and traversing is used to extend control to newly excavated areas. Control targets are typically set into stainless steel sleeves drilled into walls and used to control the LiDAR data via resectioning and point cloud registration.
Dust… and other major challenges
As mentioned, dust is a primary consideration when working in mines. Just about every mining operation creates massive amounts of fine rock dust, and this dust can be a nearly physical object–a physical point cloud, if you will, to complement the virtual point clouds produced by scanning. "If there’s thick enough dust around, the scanner will actually pick it up as a surface," Battison explains. "It’s a problem, and we can’t just wait for the dust to settle; sometimes, when it’s thickest, that’s exactly when we’re needed."
To suppress dust, mining crews spray an oil solution that adheres to the mine’s rock walls. This `clears the air’ but causes problems of its own. "We’re finding that lighting can be a problem," says Battison. "The dark oil on the walls distorts reflectivity, and scanning won’t pick up those areas accurately." Tulloch crews are sometimes forced to wash off walls with high-pressure water sprays to remove the oil that removed the dust. And sometimes the wet walls can be a problem for the scanner.
Even with dry walls and no dust, challenges remain. Mine walls are highly irregular, and the irregularities create `shadows’ in point clouds. To minimize the effect of these shadows, Battison uses unusually close setups. "With the HDS7000, we have a range of at least 120 meters (about 400 feet). But due to the wall irregularities, our setups are much closer, about 15 meters (50 feet). But it’s not a big deal; compared to total stations, we’re still moving much faster, and collecting a lot more data." In fact, Battison makes it a point to `over collect’ once he’s set up. "It only takes ten to fifteen minutes, usually, to overlap our work area, and that information can be very useful later on."
The mine itself can be a challenge; newly excavated stopes require structural support to prevent disastrous collapse. And, as always, this requires that surveyors go in first, when conditions are most dangerous, in order to do the survey work needed by structural engineers.
Fortunately, they are usually able to avoid actually entering unsupported stopes. "To avoid getting in there, we set up a series of aluminum booms, on rollers, and push the scanner into unsafe areas," Battison explains. "We can push in about 30 feet that way, which is usually enough." It also helps that scan setups are brief, and can self-register without new control being set in excavated areas.
Every surveyor needs to think about safety, but most don’t need to worry about millions of tons of honeycombed rock extending for thousands of feet overhead. Mine surveyors, by contrast, can never really forget it. Earthquakes are a good example; minor tremors that are unnoticeable on the surface tend to be major events in mines, and may precipitate urgent, well-coordinated scrambles to small, super-reinforced caverns called `refuge areas’ If a tremor is big enough, . the entire mine may be cleared.
Spending time in refuge areas, waiting for an all clear signal, is not at all uncommon in mine work and it must be a tense time, waiting and wondering if there might be another tremor on the way, one that shuts off surface access and forces miners to break out the food, water, chemical toilets, and other resources intended to last for months, if necessary.
"Actually going to a refuge due to seismic events is rare, though it’s happened to us once," says Battison. "But I couldn’t count the number of times we have left headings or arrived at a barricade heading due to tremors. We have also spent lots of time in refuge stations due to other emergencies–we have probably been sent to the refuge 4 or 5 times this year so far (as of August, 2013). The last time was because of a fire on a level above us; we were stuck for over 6 hours. Another instance this year was a frozen water line that cut off the entire water supply underground, the final outcome of this was that the entire mine was evacuated."
To qualify for underground work, Ontario miners and surveyors must complete a course sponsored by the Northern Centre for Advanced Technology (NORCAT), and must also complete a one-day, site-specific course for each mine they work in. In addition to the usual hardhats and steel-toed boots, mine workers are also required to carry cap lamps and, sometimes, air quality meters. Radios are standard; to cope with signal-inhibiting rock, mines use cable-and-amplifier-based `leaky feeder’ systems that keep everyone in touch. When working alone, which is uncommon, mineworkers may be required to set their radios for automatic `check ins’ every couple of hours. Failure to check in will lead to a search.
Fortunately, according to the Ontario Mine Association website, "Ontario is one of the safest mining jurisdictions in the world and mining is one of the safest industries in Ontario–over the past 30 years, its lost time injury frequency has improved by 90% and it is now at a level of 0.5 per 200,000 employee hours."
Working underground isn’t for everyone–every miner can tell you stories of unexpected claustrophobia in newbies–but thankfully there are plenty of people with the courage, intelligence, and resourcefulness to undertake the difficult work of extracting vital ores from underground. Their work is economically valuable, of course–Ontario mineral production is valued at about $10 billion annually–but it’s also an important aspect of human culture… as a species, we rather like electricity, and smart phones, and plumbing. The technology that mining makes possible is also applied intelligently to make mining itself possible, and the laser scanning performed by Tulloch Engineering crews is an outstanding example of that virtuous circle.
Angus W. Stocking, L.S. is a licensed land surveyor who has been writing about infrastructure since 2002. For more information about Tulloch Engineering, visit www.tulloch. ca. To learn more about surveying and laser scanning in underground mining applications, visit www.novalearningnetwork.com.
A 7.217Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE