Pit slope failure evaluation in near real-time using UAV photogrammetry and 3D limit equilibrium analysis

Slope failures are an inevitable aspect of economic pit slope designs in the mining industry. Large open pit guidelines and industry standards accept up to 30% of benches in open pits to collapse provided that they are controlled and that no personnel are at risk. Rigorous ground control measures including real time monitoring systems at TARP (trigger-action- response-plan) protocols are widely utilized to prevent personnel from being exposed to slope failure risks.

Technology and computing capability are rapidly evolving. Aerial photogrammetry techniques using UAV (unmanned aerial vehicles) enable geotechnical engineers and engineering geologists to work faster and more safely by removing themselves from potential line-of-fire near unstable slopes. Slope stability modelling software using limit equilibrium (LE) and finite element (FE) methods in three dimensions (3D) is also becoming more accessible, user-friendly and faster to operate. These key components enable geotechnical engineers to undertake site investigations, develop geotechnical models and assess slope stability faster and in more detail with less exposure to fall of ground hazards in the field.

This paper describes the rapid and robust process utilized at BHP for appraising a slope failure at an iron ore mine site in the Pilbara region of Western Australia using a combination of UAV photogrammetry and 3D slope stability models in less than a shift (i.e. less than 12 hours).