Dec '16/Jan '17

Deploying drones underground

By Ryan Preston and Darren Kennard

Ryan Preston  Darren Kennard

Accurately developing remediation plans for abandoned mines can be challenging as maps and records are sometimes sparse, if they exist at all. This is the case with the Giant mine in the Northwest Territories, which once provided a solid economic base for the local community. The mine site, however, has become a major concern since the federal government took it over when its owner, Royal Oak Mines, went into receivership in 1999. Physical stability issues, along with environmental risks, have necessitated the rehabilitation of the site.

Physical stability assessment started with the examination of historic 2D plans converted into a 3D model and validated by mine records, where possible, and by underground inspections and drilling. This model helped plan stabilization activities, including backfilling.

One major problem during this assessment, however, was the lack of accurate and complete maps of the underground workings. To make matters worse, much of the mine was unsafe for anyone to enter in order to complete the mapping.

Situations like this are common worldwide. Due partly to the expansion of communities into areas affected by historic mine sites, there is a growing need to manage the threat of ground subsidence and tunnel collapse. However, because of this danger, many abandoned mines are only safe to enter after a significant investment has been made in infrastructure, including ventilation and ground support rehabilitation.

Cavity monitoring survey systems can scan inside a void and help build a better understanding of the subsurface geometry, but these are limited in range as they need line of sight and require a borehole access.

A safer and more reliable way to map abandoned mines, which was used to plan remediation work at the Giant mine, is to use unmanned aerial vehicles (UAVs), or drones. These drones can be equipped with cameras to provide visual information to the operator, lights to assist the operator navigate the dark underground tunnels, and monitoring equipment.

So, for mining companies needing to get a better handle on their mine closure liabilities, what are some of the advantages of using drones?

For one, they are safer. The drone operator remains either outside the mine entirely, or in a section that has been determined to be safe to enter and work in.

Several years of consumer device development has made them easy to use with intuitive navigation and mapping software that has been thoroughly debugged. There are effective add-ons for mining purposes as well, such as extra-bright lights, and propeller guards and sonar systems to avoid collisions.

A complete setup including drone, camera, light and monitoring equipment can be developed for the modest sum of about $3,000. Even if the flying unit itself does get lost in a drift, it is a minor cost (drones with laser systems cost significantly more – in the area of tens of thousands of dollars).

The operator can easily gather close-up detail by flying the drone close to a rock wall to determine its condition, examine backfill to see what it is made of and in other ways provide information needed to rehabilitate the site.

Of course, all technologies have their limitations. The drone cannot be operated more than about 200 metres away, partly because of battery life and attenuation of the navigation radio signal over distance.

While drones can be operated around corners in the mine, the ability to do so is limited depending on the mine, and losing the signal may mean losing the unit. It might be that a drone could be operated out of line of sight in a room-and-pillar mine because the signal can bounce off the walls giving it multiple paths, compared to a situation where signal paths are limited. Electrical equipment in the mine can also cause signal interference.

Current research is looking at fully autonomous drones that can move around the underground environment without operator guidance, creating a map as they go. Batteries with longer life and more practical laser units are also in development.

Underground drone application is still in its infancy. During the 2016 Giant mine investigation project, surveying drones were useful for filling in some of the gaps in the mine map, supplemented with laser scanning and data gained through boreholes from surface, and proved to be a valuable new tool for underground surveying. Like any tool, however, underground drones need to be used with a clear understanding of what works and what does not.

Check out a video showing underground mine assessment using a drone at http://bit.ly/GolderDrones.

Ryan Preston, P.Eng., is a geological engineer with Golder Associates, in the Vancouver office; ryan_preston@golder.com. Darren Kennard, P. Eng., is a principal with Golder Associates, based in the company’s Vancouver office; darren_kennard@golder.com.
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