Laser technology has revolutionised surveying in mines. Maurice Jones reports
The advent of reliable lasers has revolutionised surveying practice both in terms of distance measurement and direction. More recently integration with sophisticated, high capacity control software has enabled a large amount of accurate data to be handled in short periods.
These developments allow many more ‘sightings’ to be taken automatically, resulting in complete scans of a plane or object. In underground mining and tunnelling this practice is now well established to check on the correct excavation profile or installation of lining. In mining such accuracy may not be so vital but a complete high-definition scan can also provide a complete three-dimensional picture of an excavation in much less time than would be taken by conventional surveying techniques.
Surveying safety is also improved by this technology since sightings are ‘remote’, enabling a picture to be formed of unsafe areas such as stopes and abandoned drives without exposing the survey team. An additional precautionary method is to mount the scanner on a remote-control vehicle to enter such hazardous areas.
Six-West of Belfast, Northern Ireland, undertook a recent example of mine scanning. The specialist survey firm was asked by exploration company and licence holder Dalradian Resources of Canada to carry out a complete topographical survey of the Curraghinalt gold mine in the province. Not only did the work provide such an extensive 3D picture but also Dalradian shareholders and potential investors could carry out a virtual ‘walk through’ of the mine from a desktop.
Six-West normal employs a Trimble Faro (http://europe.faro.com/en-gb/home?ext_cid=ef.aw.ge.br.uk.hp.ap) scanner or a Leica C10 (recently superseded by the Scan Station P20) to measure a 360-degree array at up to one million points per second. The latter was chosen for this task due to wet conditions.
The C10 was set up at intervals of about 50m through all the mine drives, giving 20 set-ups related to previous survey control stations established by Six-West using a Trimble S6 total station and referenced to the Irish Grid and Ordnance Survey Datum. Each full scan took 10 minutes.
Six-West used Leica Geosystems HDS Cyclone software to handle the site data to deliver final output in AutoCAD dxf, ASCII xyz and ‘flythrough’ video formats. As well as the x, y, z data scanners can also measure the intensity of reflected laser light so that lighter objects provide a better ‘return’. Thus the data can also pick up painted references on sidewalls to survey marks and geological features.
Video: Going underground: A demonstration of Leica Geosystems’ C10 Scan Station