Modern Mining October 2015

TECHNOLOGY

Drones, 3D photos and GPS take It is well known that good blast design ensures an effective distribution of powder that improves blast results and reduces drilling and blasting costs. Now, through the use of unmanned aerial vehicles (UAVs or drones), global positioning systems (GPS) and three- dimensional (3D) photogrammetric software, the field of blast design has been taken another step forward, as Tony Rorke, Technical Director of BME, explains in this article.

A t the heart of this technical ad- vance is the ability to conduct high-quality 3D face profiling using stereographic image pairs, providing accurate and detailed information for better drilling and charging designs that optimise powder distribution and reduce the risk of fly-rock. The high-quality images also provide good visual assessments and measurements of block conditions and blast results – often not achiev- able from the blast elevation or from fixed elevated viewpoints. This information is partic- ularly useful to pit-managers, mine surveyors, planning engineers and blasting consultants. Working in a number of South African mining operations – in collaboration with US expert Robert McClure of RAM Inc and Terracam (Pty) Ltd – BME has been combining these technologies to more effectively quantify blast parameters including drilling quality, block geometry, back damage, heave profile and fragmentation evaluation. The approach involves the use of small fixed-wing drones (or multi-copters to deliver oblique views) that are pre-programmed to fly a grid across a particular area of interest on the mine site. This is done before and after a blast, to create accurate and measurable 3D images for analysis. Due to the evolution of modern, high

energy-density lithium polymer batteries, UAVs have become smaller and more afford- able; and with reliable satellite navigation, they can safely fly aerial photographic surveys for up to an hour. Equipped with small, high-resolution (10-20 megapixel) digital cameras, a fixed-wing drone can fly at low altitudes and deliver high-pre- cision, geo-referenced orthophotos of the blast area. Still images are taken at intervals so that there is sufficient overlap to generate a 3D topo- graphic surface, with accuracy relying on the placement of surveyed ground control points with sufficient elevation variance. The projects in South Africa consistently achieve vertical and horizontal accuracies less than 100 mm with a minimum of four ground control points. Once this field information has been col- lected, analysis is quick and effective; by incorporating the options into a single pack- age, a mine can manage their site with more confidence – making decisions with the most up-to-date information. Two software applica- tions are required: one to generate a 3D surface orthophoto from the UAV images, by creating dense and filtered 3D data in any format from ASCII point clouds to raster GeoTIFFs or ECWs; and survey software to analyse volumes, cut- lines and surfaces. The type of blast-specific information obtained from the photographs are: pre-blast

BME’s Tony Rorke.

32  MODERN MINING  October 2015