Rockfall hazard mitigation on infrastructures in volcanic slopes using computer-modelled ditches

Rockfalls on transport infrastructures are a serious hazard to users and many resources are invested in rock slope maintenance, stabilization, and protective measures. In volcanic territories, the risk of rock instabilities and rockfalls is very high due to the rugged natural slopes and origin of rock masses. With the aim of determining the influence of the geometric and material-related properties affecting rockfall motion and the effectiveness of catchment area design criteria, this study applies a computer simulation model considering 150 different slope configurations and ditch geometries, 4 types of materials and 9 size and shape combinations of falling rocks. A statistical analysis of the simulated rock stop-distances was performed. Results show that density, hardness, roundness and size are material properties directly correlated with the rockfall stop-distance. However, block accumulation distribution differs with the rock hardness. Furthermore, practical application design charts are proposed for infrastructure planning and design tasks. These offer the ditch dimensions depending on the relation between the optimal stop-distance and the cumulative percentage retained along the trajectory, complying with specific retention requirements, and optimize the dimensions of previous studies. A triangular ditch of foreslope steepness 14 degrees offered better retention capacity and road safety than a deep flat-bottom ditch. These rockfall protection areas constitute non-structural defence measures of reduced environmental impact and cost in volcanic territories.