Improved Management Of The Rock Fall Hazard At The Base Of The Highwalls

Rockfalls are a significant safety hazard in open pit mines and underground mine entries from open cut highwalls. The project aimed to gather coal-mine specific data on rock falls with and without rock fall netting, and to outline a more rigorous approach to the design of face bolting, rock fall netting and portal protection structures. An integrated approach was followed where the major components of rockfall hazard at a given mine site were rigorously assessed.

Through a reliable description of unstable block size, a numerical estimation of trajectories, velocities and run-out distances validated against existing rockfall event records and field experiments the work undertaken during this project resulted in a methodology to properly estimate the fundamental characteristics of a rockfall event in the mining environment (volume, shape, slope profile, coefficient of restitutions, velocities).

The results highlighted the effect of the restraining net on the block trajectories and impact energies. It was found that rockfall impact velocities on top of the portals are reduced by about 50%, which is less than previously anticipated without this field work. It was also observed that the netting restrained impacts close to the highwall with an impact zone on top of the portal reduced by more than 60%.

The outlined approach to site investigation and data collection could be considered in the future in different mine sites with rockfall protective measures already installed in order to control their efficacy or to optimize the design of new rockfall protection installations.

The study emphasized some implications/improvements on the design of portal and complementary remediation measures such as muck piles which have a key role to play in the current highwall entry strategies. A new rigorous geotechnical approach for the design of the muck piles will be examined in the ACARP project C21032 commenced in 2012.

An e-newsletter has also been published for this project, highlighting its significance for the industry.