Global characterization of high rock slopes using the hoek-brown mb parameter as controlling index

One of the most iconic graphs in rock engineering is the slope height versus slope angle chart (Lutton 1970; Hoek & Bray 1981). Many large open pits and high rock cuts have been designed with this chart providing geometrical benchmarking. However, it has long been recognized that the limit lines that have been traditionally drawn on these types of charts are flawed with respect to prediction of maximum credible slope heights for high competence rock masses. A new empirically-based chart, which largely addresses this restriction was proposed at the 2018 Large Open Pit Symposium in Sevilla, Spain (Carter 2018). To achieve better matching to the complete spectrum of precedent high natural and man-made slopes, this new chart was formulated using the Hoek-Brown mb parameter as a measure for subdividing the data into a family of Jaeger- style U-shaped critical angle curves, rather than the more usual negative exponential. This paper explores the shape of the mb-trendlines established in the empirical chart in Carter (2018) and introduces a theoretically based suite of slope height versus slope angle analytical curves calibrated to the data presented earlier on. It is hoped that this new set of curves will assist for better slope benchmarking.