Rockfall Catchment Investigations for the Upper West Wall of the Valley Pit

2016

Dr Gustavo Gonzaga (Senior Geotechnical Engineer - Piteau Associates), Mr Mathieu Veillette (Senior Geotechnical Engineer - Teck Highland Valley Copper), Mr Nick Rose (Vice President - Geotechnical - Piteau Associates)

Deep-seated toppling deformation and structural breakback along persistent moderately-dipping joint sets has resulted in reduced rockfall catchment on the upper west wall of the Valley Pit at the Teck Resource’s Highland Valley Copper (HVC) mine near Logan Lake, BC. To improve rockfall catchment conditions, a rockfall study was undertaken that included controlled rockfall field testing to allow calibration of rockfall model restitution coefficients and design of rockfall catchment measures. The calibration process utilized a statistical approach where cumulative percent rockfall retention curves from actual field tests were matched to the simulated results from rockfall modelling. The calibrated modelling results were used to forecast rockfall conditions and to develop standardized rockfall retention design charts for the Valley Pit. Revisions to the bench designs on the upper west wall have reduced rockfall hazards and greatly improved working conditions. Rockfall retention design charts developed for bench face angles (BFAs) ranging from 55 to 70° were compared to the bench catchment widths defined by the Modified Ritchie Criteria (Call, 1992). This comparison revealed that bench catchment widths assessed with the Modified Ritchie Criteria for benches without a rockfall impact berm would result in retention of about 95% for BFAs steeper than 70°, but less than 70% for BFAs less than 65°. This suggests that caution should be used when applying the Modified Ritchie Criteria to the design of benches that are subject to shallow breakback angles that may result in significant filling with debris over time, and rockfall events that are dominated by rolling.