Rockfall is an extremely rapid process involving long travel distances. Due to these features, when an event occurs, the ability to take evasive action is practically zero and, thus, the risk of injury or loss of life is high. Damage to buildings and infrastructure is quite likely. In many cases, therefore, suitable protection measures are necessary. This contribution provides an overview of previous and current research on the main topics related to rockfall. It covers the onset of rockfall and runout modelling approaches, as well as hazard zoning and protection measures. It is the aim of this article to provide an in-depth knowledge base for researchers and practitioners involved in projects dealing with the rockfall protection of infrastructures, who may work in the fields of civil or environmental engineering, risk and safety, the earth and natural sciences.

Models can be useful tools to assess the risk posed by rockfall throughout relatively large mountainous areas (>500 km²), in order to improve protection of endangered residential areas and infrastructure. Therefore the purpose of this study was to summarize existing rockfall models and to propose modifications to make them suitable for predicting rockfall at a regional scale. First, the basic mechanics of rockfall are summarized, including knowledge of the main modes of motion: falling, bouncing and rolling. Secondly, existing models are divided in three groups: (1) empirical models, (2) process-based models and (3) Geophysical Information System (GIS)-based models. For each model type its basic principles and ability to predict rockfall runout zones are summarized. The final part is a discussion of how a model for predicting rockfall runout zones at a regional scale should be developed. A GIS-based distribution model is suggested that combines a detailed process-based model and a GIS. Potential rockfall source areas and falltracks are calculated by the GIS component of the model and the rockfall runout zones are calculated by the process-based component. In addition to this model, methods for the estimation of model parameters values at a regional scale have to be developed.

Only a few rockfall simulation models take into account the mitigating effect of existing forest cover. The objective of our study was to improve the generic rockfall simulation model RockyFor, which does take the effect of forest stands into account, thereby developing a clear method for quantifying and modelling slope surface characteristics based on quantitative field data. To obtain these data we carried out 218 real-size rockfall experiments on forested and non-forested sites on a mountain slope in the French Alps. On the basis of a polygon map representing different diameter classes of the material covering the slope, we determine the mean obstacle height (MOH) for each homogeneous unit at the experimental sites. We proposed an algorithm for calculating the tangential coefficient of restitution using the MOH. Comparing the simulated and observed data from the real-size rockfall experiments showed that the 3-D combined deterministic-probabilistic rockfall simulation model RockyFor accurately predicted rockfall events on a non-forested (Root Mean Square Error = 17%) and a forested site (Root Mean Square Error = 12%). We conclude that for further improvement of rockfall-forest simulation on different slope types more quantitative data is required on (1) the energy dissipative capacity of shrubs and bushes (e.g. in coppice stands), (2) the effect of the slope material, (3) the rock shape as well as the rock size, and (4) the tangential and normal coefficient of restitution. Based on the presented results we can state that the RockyFor model could contribute to better taking into account the mitigating effect of the existing forest cover when planning protective measures.