Effect of Impact Angle and Rotational Motion of Spherical Blocks on the Coefficients of Restitution for Rockfalls

The coefficients of restitution are among the most important parameters in rockfall trajectory modelling. However, they are difficult to obtain, they depend on many parameters and they present a significant variation even for similar geotechnical and kinematic conditions. Many definitions for the coefficients of restitution exist, but there is no agreement on which describes better the response of a block to an impact. In this paper, an extensive experimental investigation is presented, consisting of 600 oblique impact tests and the various coefficient of restitution definitions are assessed, with an emphasis on the effects of impact angle and angular velocity. These tests follow on the research presented in Asteriou and Tsiambaos (Int J Rock Mech Min Sci 106:41-50, 2018), where free-fall tests were performed to address the effects of impact velocity, block mass and material type. It was found that all those parameters affect significantly the coefficients of restitution. Moreover, an empirical model was proposed to estimate the coefficient of restitution for central impacts. The applicability of this model is extended for oblique impacts based on the results of the tests presented in this paper.