Rockfall Barrier Testing in an Open Pit Mine: Comparing Empirical and Modeled Rockfall Dynamics

ABSTRACT: Rockfalls pose severe hazards to miners and infrastructure in open pit mines, and rockfall barrier systems are an increasingly common method for mitigating this hazard. Extensive testing to understand rockfall kinetics and barrier efficacy has been performed in controlled settings and natural environments, but rarely in open pit mining environments. This study is part of a collaboration with the National Institute for Occupational Safety and Health, Geobrugg, and the University of Arizona's Geotechnical Center of Excellence, in which controlled rockfall tests were conducted using synthetic concrete rocks on an open pit highwall with a prototype mobile rockfall barrier system. A solitary rockfall that impacted the barrier with significant force was analyzed to determine the kinetics and kinematics of its fall trajectory leading to the barrier strike. These results are then compared to a best-fit 2D rockfall simulation, showing a close match at the moment of impact into the barrier. Lastly, the effects of highwall bench configuration on the test rock trajectory are assessed, which suggest that minor catch bench loss likely resulted in the test rock attaining dangerously high velocity and lateral trajectory, ultimately sending it into the barrier. 1. INTRODUCTION Engineering advancements in open pit mining and the ever-growing demand for critical minerals have led to increasingly large open pits, characterized by highwalls thousands of feet tall. This expansion necessitates robust slope monitoring techniques to ensure the safe execution of mining operations. Significant improvements in slope monitoring techniques have enabled a step change in miner safety that allows mining activities to proceed concurrently with active slope movements, provided that critical thresholds are not exceeded (e.g. Carlà et al., 2017; Farina et al., 2013). However, in contrast to the notable progress in monitoring for movements from inches per day to inches per year, monitoring of rapid movement due to rockfall in open pit mining has not seen similar advancements to slope monitoring, presenting a significant and inadequately addressed hazard to miners, equipment, and infrastructure. Engineered barriers are often the last line of defense when attempting to mitigate against rockfall, and their efficacy is of critical importance to personnel or infrastructure relying on the barriers for protection. Extensive rockfall barrier testing has been performed on natural slopes (e.g. Jaboyedoff et al., 2005; Sanchez & Caviezel, 2020), man-made fill slopes (e.g. Williams et al., 2020), vertical drop (e.g. Gerber, 2001), or by numerical modelling (e.g. Mentani et al., 2016; Spadari et al., 2012) to test and assess their efficacy. Despite the great need for rockfall protection in open pit mining environments, rockfall testing rarely occurs on open pit mine highwalls where the effects of benched geometries, which are designed to stop falling rock, can be evaluated with respect to rockfall kinetics.