Objectives:
This project evaluates rockfall risk and bench design in open pit mining to determine how mine operators can demonstrate that rockfall hazards have been reduced to ALARP (As Low As Reasonably Practicable). It presents four case studies that apply quantitative rockfall risk assessment methods and compare estimated risks against commonly used individual and societal risk tolerability criteria. The study shows that rockfall risk depends on more than bench retention performance alone. Risk is influenced by rockfall frequency, runout behaviour, worker and equipment exposure, vulnerability, and the effectiveness of mitigation measures. Quantitative assessments using change detection from LiDAR or UAV surveys, rockfall trajectory modelling, monitoring systems, and exposure analysis provide a practical and defensible framework for assessing risk.
Cases 1 and 2 demonstrate established methods for hazard mapping and risk calculation, including F-N risk curves and time-space probability concepts. These studies show that controls such as monitoring, catch benches and depressurisation can substantially reduce fatality risk and support demonstration of ALARP. Cases 3 and 4 highlight the strong influence of geological and environmental conditions on rockfall frequency. Although both sites achieved bench retention levels commonly considered acceptable, Case 3 experienced much higher rockfall activity and significantly greater risk. This demonstrates that meeting retention criteria alone does not necessarily result in tolerable risk levels.
The project shows that quantitative risk assessment should form a key component of bench design and operational decision-making. Measures such as exclusion zones, windrows, monitoring systems and enhanced retention controls can reduce risk by up to an order of magnitude and provide robust evidence that rockfall risk has been reduced to ALARP. The report recommends expanding change-detection studies across a wider range of pit environments and improving exposure data collection to support future design acceptance criteria and more effective rockfall risk management.