Open-Pit Surface Operation: Cavity Scan
Not for disclosure
Northern Cape, South Africa
Type of Scan
Migrating from the unknown to the known with Emesent Hovermap
In an irregular event, a cavity appeared after a blast on surface at a South African open pit Iron Ore operation. To mitigate subsequent risk the mine needed to understand the ground conditions and cavity dimensions, specifically how far the cavity extended and to ultimately understand potential reasons for the cause for the cavity. The mine also needed to collect adequate data to determine if it was safe for mine personnel to proceed with mining activities in the direction of the cavity specifically on top of the bench where drilling had taken place.
Since the cavity was inaccessible and unsafe to attempt using conventional survey methods to investigate it, the mine initially opted to use a Light Detection and Ranging (LiDAR) scanner together with a drone to get a point cloud and video footage of the cavity. The cavity however created a pseudo-underground environment, which limited access and inhibited the use of Global Positioning System (GPS) for drone navigation. This meant that the mine could only retrieve limited point cloud data from the outside of the cavity as shown in Figure 1-2.
Figure 1 Top view- outside of the Cavity
Figure 2 Side view- Outside of the cavity
The primary goal was to ascertain the geometries and volumetrics of the cavity. In order for the mine to collect this data from inside the cavity, Dwyka Mining Services as local suppliers of Emesent’s HovermapTM from Brisbane Australia were engaged to assist. HovermapTM is a unique on- and off-drone payload that provides LiDAR mapping, omnidirectional collision avoidance, GPS-denied flight and advanced autonomy when attached to a drone, which allows for a number of underground mining use cases and in this instance allowed the mine to map the inside of the cavity without the need of GPS.
The secondary goal of the scan was to achieve a clear conceptual view of the geological and geotechnical data from inside the cavity. With the capability of the HovermapTM to collect high density coverage, delivering 300,000 points per second(p/s), multiple 3D point clouds were captured and merged to depict the abovementioned data. Hovermap™ utilises the most advanced global Simultaneous Localisation and Mapping (SLAM) algorithms for mobile capture instead of traditional terrestrial and GPS/INS hardware. This LiDAR data was logged on-board the Hovermap™ and post-processed to produce geo-referenced 3D point clouds.
Figure 3 HovermapTM& Drone
Figure 4 HovermapTM point cloud-front view of the cavity
Figure 5 HovermapTM Cavity scan with trajectory file
Figure 6 Rock structures inside the cavity
Figure 7 Roof of the cavity
Figure 8 Width of the cavity
Figure 9 Length of the cavity
Figure 10 Top View with Cavity Superimposed
Figure 11 Aerial View of Affected Mining Area
Collaborative effort with client, empowered with the HovermapTM and drone platform was successful in delivering a high density point scan (300 000 p/s) after a single 5-minute flight which enabled the successful mapping of the inside of the cavity unlocking previously inaccessible geometries and internal condition evaluation.
The point cloud of the inside of the cavity produced by the HovermapTM SLAM technology is shown in Figure 4-7. Hovermap™ SLAM technology is linked to the trajectory (Note: See flight path in the various images) of the drone together with the HovermapTM as it mapped the cavity. The width of the cavity was measured using point cloud software Cloud Compare as 62.6m while the length of the cavity internally was measured to be 91.1m. Various assessments were also generated by client in their third party software suite following export of the *.laz file.
The added visualisation capability from a geotechnical standpoint confirmed that the cavity did not extend further and to mitigate risk would now form the extent of the mining processes in the pit.
Client Quote: “Using technology such as the Hovermap empowered our teams with certainty as we used the visuals to move from a position of unknown to known. We expect that the use cases of this technology for assurance and safe mine planning as well as indoor digital twinning in GPS-denied environments to rapidly evolve. We will be watching this with great interest even as a surface operation with the user-friendly operation and flexibility of the solution”.