The Impact of Slope Roughness on the Uncertainty in Probabilistic Rockfall Modelling

Rockfall simulations play a crucial role in assessing rockfall hazards and designing mitigation measures. A very common approach in industry is to perform probabilistic rockfall simulations on the basis of idealized 2D profiles. Highwalls in open cuts are generally considered as a single slope segment with artificially introduced roughness. This study assesses the uncertainty associated with such single slope profile rockfall simulations with respect to the energy at first impact at the base of the wall as well as runout distance. The results of single slope rockfall simulations are compared against simulations performed using sophisticated 2D sections extracted from four different photogrammetric derived 3D high-resolution rock wall models. In the results, it is shown that the energy at first impact is similar for both simplified and natural slopes but with higher variability of energy for natural slopes. In contrast, the runout distances are always underestimated by the simplified slopes compared to natural slopes. These disparities are associated with the inability of simplified single-line-segment slopes to accurately represent the irregularity in natural slopes. Hence, the results indicate the importance of rockfall simulations performed with slopes extracted from high-resolution 3D models for more realistic results.

Keywords: Probabilistic modelling, Rockfalls, Runout distance, Surface roughness, Lumped mass model.