Mining Project: Open Pit Highwall Safety

Research Summary

This pilot project research addressed two issues that are fundamental to open pit highwall mining: rockfall catchment and slope monitoring.

Rockfall hazards in open pit mines are a constant threat to mine workers and are typically addressed by catch benches—horizontal spaces set in from the highwall to retain rock spillage—as mandated by the Mine Safety and Health Administration (MSHA). Current catch bench width design criteria for open pit mines were developed in the early 1970s and little work has been done since to improve these guidelines. Industry geotechnical engineers have expressed the desire to revisit the established guidelines to better balance rockfall catchment performance and pit economics, or at least to quantify the performance of current methods. Acceptable rockfall risks vary depending on exposure levels of workers and nearby critical infrastructure. In addition, rockfall risk tolerances can change over time as mining progresses, creating “temporary” slopes that have low human exposure and necessitating the development of portals and workforce offices at the base of existing slopes.

Recent developments in slope monitoring radar have greatly improved the ability to monitor and quantify slope movements. However, these systems are more complicated than traditional monitoring methods and require greater technical knowledge to operate. Additionally, few engineers charged with running slope radar are given the time and training necessary to understand the subtleties and limitations of the systems. For example, setting slope movement alarm rates for pit evacuation is not trivial, and mistakes in setting these alarms can unnecessarily jeopardize the safety of the workforce. The 2013 slope failure at Bingham Canyon represents a successful application of slope monitoring technology by sufficiently defining the timing of the slope failure in order to balance production and safety. However, several severe near-miss slope failures in the U.S, which could have been termed “mine disasters” in relation to fatality counts, have highlighted the need for industry training, standards, and guidance on setting slope movement thresholds for pit evacuation.

NIOSH researchers involved in this one-year pilot project addressed these issues by way of literature review, slope failure database analysis, mine visits evaluating the current state of practice, rockfall field testing, and data analysis based on that field testing. Success of this research was measured by tracking of industry bench design by way of mine site visits and discussions with top industry consultants. The results of this project were used to plan a more targeted and in-depth follow-on project.