Rock catchment area design charts

Abstract

Studies on the effectiveness of deep ditches against rockfalls have shown that, the original Ritchie (1963) guidelines are not as conservative as previously thought. Moreover, following these guidelines, a unique ditch "depth - width" pair of values is obtained for a given rock cutting not allowing for the chosen of the most economical solution. The above findings gave rise to the research presented herein, where, a number of design charts based on a computer simulation program (RocFallTM) are proposed for deep rockfall ditches. Rockfall concrete walls and fences became also subject of research as there are no relevant design charts currently available. The assumptions made for the derivation of the proposed charts are: a) the number of falling rocks is one hundred, b) the rocks are detached from the slope crest, c) the initial speed of falling rocks is zero, d) the material of slope is a clean hard bedrock and e) the base of the catchment area is covered by a layer of gravel to absorb the energy of falling rocks. For the case of deep rockfall ditches it was additionally assumed that, the ditch foreslope adjacent to the roadway is vegetated. Furthermore, as a cut slope can be of any rock type and thus, charts of this category provide indicative dimensions, the RocFallTM default material settings (e.g. coefficient of restitution) were adopted. Finally, it is noted that, for the simple geometries studied using RocFallTM (slopes without outcrops and benches) the rock impact distance was always zero and therefore, the calculated catchment area width should be corrected adding the maximum impact distance of rocks obtained by Pierson et al. (2001) empirical study.