Calibration of rock fall modeling parameters

• The paper discusses the calibration of parameters used in rock fall modeling based on field data and impact mechanics.
• The fundamentals of impact mechanics are discussed to define the relationship between impulse and velocity during impact.
• The field data are from Canada, the United States and Japan, for rock, talus, colluvium and asphalt surfaces.
• The field data have been analyzed to determine the normal and tangential coefficients of restitution, eN and eT.
• The results show that eN can have values greater than 1.0 for shallow impacts, and eN is not a material property.

Rock falls can be a hazard for many facilities in mountainous terrain, particularly in areas with high rainfall and freezing temperatures, and where seismic events occur. Design of protection measures against rock falls, such as fences, barriers and sheds requires information on impact energy to determine the strength of the structure, and on trajectories to determine its location and size. This paper presents documentation on rock falls at five locations, in North America and Japan, involving impacts on rock, talus, colluvium, asphalt and concrete, for which values of the normal and tangential coefficients of restitution have been calculated. The field results show that the normal coefficient of restitution is related to the impact angle with coefficients of about 0.2 for normal impacts and values as great as 2.5 for shallow impacts. These values for the normal coefficient of restitution are essentially independent of the slope material. The tangential coefficient of restitution ranges between 0.3 and 0.8 and is related to the friction coefficient at the impact point, and is independent of the velocity and normal force. It is also shown that the calculated field values for the coefficients of restitution are consistent with the principles of impact mechanics.