Rockfall in open pit mines: management of the pit geometry and protection measures design

Rockfall events represent a serious hazard for people, structures, and infrastructures. The phenomenon can occur in several environments, natural and artificial. In surface mining operations, blasting, bench clean-up and scaling can induce rock blocks detachment, compromising operators’ and operations’ safety. The installation of passive mitigation measures coupled with a specific design of the pit geometry can mitigate this risk. The bench height, width, and slope angle, the number of benches, together with the material characterizing the slope, affect in different ways the kinematics of the possible detached blocks. In this paper, a large set of configurations is studied and trajectory analyses are performed to evaluate the influence of each geometrical or material variable. Results are analysed considering blocks kinematics both on the pit floor and at each bench. The findings provide a useful a tool for a preliminary design of pit geometry and mitigation measures. Design charts are proposed for different slope materials, reporting, as function of the total pit height, the blocks stopping distance, their velocity at the pit floor, their passing height and velocity at each bench, for each geometrical configuration. The obtained charts can be effectively implemented in a quantitative risk assessment procedure for mining activities.