Rockfall run-out estimate comparing empirical and trajectographic approaches

Rockfall hazard comes from two processes: detachment of rock blocks from the upper part of the cliff, and their propagation along the lower part of the slope. Several hazard approaches attempt to assess the probability of propagation, for an assigned rockfall magnitude class, stopping at a specific point from the source area. The probability of reach is evaluated by trajectory simulations, from the distribution of the blocks deposited along the slope, or by empirical approaches such as the reach angle and/or the shadow angle. The aim of this paper is to compare the results of rockfall travel distances calculated by means of two methods for a cliff impending over a viaduct near the harbour of Salerno. Using the reach angle model, a first scenario was prepared showing three reach probability boundary lines. Using trajectory simulations, another rockfall hazard scenario based on kinetic iso-energy curves was then drawn. Comparison of the two hazard scenarios shows several differences, subsequently analysed in detail.