Temporal-Spatial Frequency Rockfall Data from Open-Pit Highwalls Using a Low-Cost Monitoring System

Abstract

In surface mining, rockfall can seriously threaten the safety of personnel located at the base of highwalls and cause serious damage to equipment and machinery. Close-range photogrammetry for the continuous monitoring of rock surfaces represents a valid tool to efficiently assess the potential rockfall hazard and estimate the risk in the affected areas. This work presents an autonomous terrestrial stereo-pair photogrammetric monitoring system developed to observe volumes falling from sub-vertical rock faces located in surface mining environments. The system has the versatility for rapid installation and quick relocation in areas often constrained by accessibility and safety issues and it has the robustness to tolerate the rough environmental conditions typical of mining operations. It allows the collection of synchronised images at different periods with high-sensitivity digital single-lens reflex cameras, producing accurate digital surface models (DSM) of the rock face. Comparisons between successive DSMs can detect detachments and surface movements during defined observation periods. Detailed analysis of the changes in the rock surface, volumes and frequency of the rocks dislodging from the sub-vertical rock surfaces can provide accurate information on event magnitude and return period at very reasonable cost and, therefore, can generate the necessary data for a detailed inventory of the rockfall spatial-temporal occurrence and magnitude. The system was first validated in a trial site, and then applied on a mine site located in NSW (Australia). Results were analysed in terms of multi-temporal data acquired over a period of seven weeks. The excellent detail of the data allowed trends in rockfall event to be correlated to lithology and rainfall events, demonstrating the capability of the system to generate useful data that would otherwise require extended periods of direct observation.

An Optimum Deployment Algorithm of Camera Networks for Open-Pit Mine Slope Monitoring

“…Due to topographical and other shading issues at the mine site, the use of front-to-surface photography may result in missing images in some areas that cannot be reconstructed in 3D, so the observation platform should be selected with due consideration of whether the area to be observed can be captured by all of the corresponding cameras. Considering the actual cost of the project, the low-cost solution of camera photogrammetry is easy to accept for small and medium-sized mines [ 7 , 21 ]. Additionally, our solution allows for automated monitoring after deployment, which also reduces the investment in manpower costs for the mine.…”

“…Among the methods applied for open-pit mine monitoring, the close-up photogrammetry technique is a moderate method which can provide high efficiency and inexpensive measurement, especially compared to the other usual methods of laser scanning, the Interferometric Synthetic Aperture Radar (InSAR), the Laser Radar (LiDAR), etc. [ 19 , 20 , 21 ]. The use of photogrammetry has the requirement of capturing images with a degree of overlap, which places demands on the deployment of cameras.…”

“…The intelligent application of multicamera video data in mining is an important aspect of smart mine constructions, and a number of studies have applied photogrammetry to the digitization of mines [ 27 ], reconstructing visual data in three dimensions and measuring parameters such as slope deformation monitoring and the slope gradient. Giacomini et al [ 21 ] used close-up photogrammetry to continuously monitor the rock surface, in order to assess the potential rockfall risk and estimate the area of impact. Aggarwal et al [ 28 ] implemented an Internet of Things (IOT) landslide monitoring system based on Raspberry Pi using a camera.…”

Photogrammetric Digital Surface Model Reconstruction in Extreme Low-Light Environments

“…Images acquired by three fixed terrestrial monitoring systems were considered in this paper. One system, thoroughly described in [29], was installed in front of an artificially excavated rock face in a surface mine site in Australia, while the other two were set up in front of two natural rock slopes in Italy.…”

“…A fixed photogrammetric monitoring system, designed for the monitoring of rockfalls in surface mining [29], was chosen to ensure the highest control and repeatability of the acquisition. The system consists of two stand-alone units that acquire images simultaneously at scheduled times.…”