SIMON ARTHUR and DAVID ELDRIDGE

In an effort to enhance mine safety, the management of Beaconsfield gold mine, at Beaconsfield in north eastern Tasmania, has purchased a new laser scanning system. It can rapidly scan the underground workings. What’s more, it is remote-controlled, so the operators are never exposed to danger.

Historically, Beaconsfield’s mine surveying team has been restricted to using older technologies such as cavity monitoring systems, which have been around for 10-15 years. These systems are slow, require two men to operate the equipment, and collect a limited amount of data. Access to the restricted stopes (the caverns where the ore is mined) is limited by the boom length of the equipment. Visibility of the area beyond is virtually impossible.

After the serious incident underground on Anzac Day in 2006 (See Position 24, August 2006, pp. 10-11), management has been single-minded in its determination to improve safety in the mine.

To safely extract ore, it is necessary to mine tunnels to access the ore body above existing tunnels that can no longer be accessed. These ones were mined parallel to the existing drives so that production drilling could take place. The ore was then removed through draw points by remote controlled extracting equipment.

We were about to introduce a new model of these so-called boggers, a CAT R1300G mining loader, as part of the safety improvement program. With this in mind, we were also keen to find a way in which to improve the safety of surveys. We had heard about some new laser scanning technology and we were interested to see whether this could be applied to the conditions at Beaconsfield.

At this point, the Beaconsfield team approached Hi-Tech Metrology, a Melbourne company that represents the laser scanner manufacturer Faro Technologies in Australia.

The product chosen for the application, Faro’s LS-880 laser scanning system, is a 3D spatial information capturing system. It collects data at a rate of 120,000 points per second at a distance of up to 80 metres from the scanner. The accuracy of the scan data collected is quoted as +/-3 mm over a 25 metre distance.

It is motor-driven on a horizontal axis, which gives it a 360 degree field of view in the horizontal plane and a 320 degree field of view in the vertical plane.

Our first plan was to use a specially designed, remote-controlled buggy to send the scanner into the inaccessible stope area. Faro has done this overseas. We were keen to use the tele-remote loader as the means of delivering the scanner into the mine stopes.

This presented some challenges to the development team, which consisted of members from Beaconsfield’s survey, electrical and maintenance groups, and Hi-Tech Metrology.

Initially, it was thought that the major challenges would be excessive vibration, water and dust, plus potential damage from rock falls, but these issues were resolved relatively easily. Our underground maintenance team developed a special-purpose box to house the laser scanner, which was mounted inside the loader bucket using a gimbal mounting system. They also built special isolation mounts to fix the scanner to the mounting box. This minimised vibration transfer from the box to the scanner assembly.

Providing a communications channel between the laser scanner in the loader bucket and the operator’s station was a much bigger problem. There were two options. One was to use an extra channel on the bogger’s existing analogue communications system. An alternative was to provide an expendable cable system along the tunnel.

Neither of these options was ideal. It was desirable to control the remote scanning of a stope independently of the loader, even though the scanner was mounted in the bucket of the loader. This required wireless communications from the loader back to a remote laptop computer.

We eventually solved the communications issues with Rajant Technologies’ Breadcrumb wi-fi product, supplied locally by Mine Site Technologies.

Using these Breadcrumb units, we established a wi-fi mesh underground. It consists of a Breadcrumb personal unit mounted in the cabin of the loader and connected by a CAT5 cable to the scanner and its mobile battery pack. Another two Breadcrumb units hang from the walls of the drives, allowing wireless communications back to a remote laptop computer at the control station. This telemetry was used to both upload data and operate the scanner.

The wi-fi network requires line-of-sight between the Breadcrumb units. The distance between the operator and the stope being surveyed can be up to several hundred metres away and on different mining horizons or levels. We purchased three units.

When work recommenced, achieving line-of-sight was not an issue. However, as the drives advanced and the distance between the remote bogger operator and the stope increased, achieving lineof- sight became progressively more difficult.

After consultation with the electrical department, a system using Cat5 LAN cabling run from the operator station to the footwall drive and two VDSL (Very high bit-rate Digital Line Subscriber) routers were constructed to extend the range of the system.

The scanner needs to be positioned at different points to enable the surveyor to develop a complete picture of the inside of the workings. It is essential to be able to instruct the bogger operator where to position the bogger for each of the scans. Using the communication system devised and the Web interface between the scanner and the laptop, it is possible to view each scan as it is produced, and so build a complete picture.

After a number of underground trials, the system was proven to the satisfaction of management. The team then moved on to the next phase; data processing.

The enormous amount of spatial data collected by the scanner needs to be processed in the software supplied with the scanner, a product called Faro Scene. It registers the multiple scans taken in a session, imports the co-ordinates of the reference points along the drives that have been picked up with a total station during surveying, and filters any extraneous data.

The process of registering the multiple scans is similar to that of rectifying aerial photographs to produce an orthophoto or map.

Once the scans are registered, processed and reduced in size, the data is converted to a triangulated STL mesh format for export. The files are then exported in a DXF file format, which can be imported into the mine’s CAD system, currently Gemcom’s Surpac 6.02.

At Beaconsfield, the data is used to supply several important metrics. Volume calculations can be made of the material that has been removed from the stope. This can be compared to both the theoretical volume and the amount of material the mining group claims to have removed for the month.

The survey data is kept on the survey files as a number of cross-sections, not unlike those generated as a result of a conventional CMS survey.

There are other significant benefits of this technology. Because of the data clarity, geotechnical engineers can reliably assess the safety or otherwise of the stope area. This authorisation is a key part of Beaconsfield’s enhanced safety programs at the mine.

Surveying underground is now a oneman operation, as opposed to the twopeople operation previously needed with the CMS. This is a real cost saving for the mine.

Laser scanning offers significantly faster data collection and far better stope visualisation tools than the CMS. It takes about three minutes to scan a stope. This is fast enough to enable site personnel to determine if ore is still to be extracted.

It can also be used to assess stopes where the mining has been incomplete. This allows the mining groups to make decisions on whether to go back into the stope and recommence bogging.

While our experience with laser scanning is still in its early stages, the management of the mine have already seen the benefits of the use of this technology and are keen to apply it to other applications, now that the equipment is on-site and personnel are experienced in its use. It could potentially be used for surveying other parts of the mine, such as its decline, and for use in walk-through animations and 3D models for visitors and other interested parties.

We have used the scanner for other more traditional tasks, such as scanning underground plant and equipment to develop as-built drawings. This is also useful for assessing whether new plant and equipment will fit into the available areas, without the cost and time of actually taking the plant and equipment underground. Survey applications on the surface are also possible, including plant infrastructure, as well as in the mill and ore processing plants.

We are continually enhancing the application of laser scanning at Beaconsfield. Current applications include additional scanning protection systems, more communications options, and future delivery systems for the scanner in underground applications where tele-remote equipment is unavailable or unsuitable for the particular situation.

These developments will ensure that the groundbreaking achievements made at Beaconsfield Gold Mine continue to provide financial benefits and enhanced operational safety. They also stand as a great testament to the ingenuity of the industry in applying innovative technologies in a novel way.

Simon Arthur is the chief surveyor at Beaconsfield gold mine. David Eldridge is the general manager of Hi-Tech Metrology in Melbourne.

 
Issue 38; December 2008 – January 2009