Analysing slope stiffness effects on rockfall fragmentation using a new stochastic rockfall fragmentation approach for lumped mass simulations

A stochastic fragmentation approach for rockfall applications, based on experimental and numerical observations, has been developed. Extensive experimental campaigns on artificial spherical rock-like specimens revealed key aspects of block fragmentation upon impact, including patterns and relationships between fragment characteristics and impact velocity. The authors proposed the first stochastic fragmentation prediction model, based on the statistical distribution of material properties of both the impacting and impacted materials. Numerical studies using marble spheres suggested a model to consider cumulative damage (caused by previous impacts) in the energy required to break the falling block. These findings were incorporated into a lumped mass trajectory simulator, NURock, developed at The University of Newcastle. This paper presents the application of the new fragmentation approach with a focus on the influence of slope stiffness on the rockfall fragmentation outcome. The simulations using NURock are compared to unfragmented simulations using RocFall2. The results showed how harder rock slopes resulted in more rockfall fragmentation, hence less energy and shorter run-out distances. The results demonstrate that accounting for block fragmentation and cumulative damage can significantly alter the design of protection structures, as the size of blocks reaching a given risk zone can be much smaller compared to unfragmented simulations.