Towards the comprehension of rockfall motion, with the aid of in situ tests

Abstract

Rockfalls frequently occur in Alpine areas, creating serious risks to population and buildings; the protection measures against rockfalls cannot be adequately designed unless the comprehensive understanding of rockfall phenomenon. Some experimental rockfall tests have been performed on a talus slope in Grosina Valley (northern Italy), with the aim to check the reliability of common simulation methods and to analyse the motion of falling blocks. First, apriori kinematic simulations have been performed, and, after the rockfall tests, the results have been compared with the real stopping positions of blocks. Afterwards, the recorded trajectories of falling blocks have been analysed, allowing the calculation of the motion parameters of falling blocks. The motion of blocks was mainly characterized by rebounds, therefore particular attention has been paid to restitution coefficients, which describe the loss of energy during the impact and greatly affect the results of rockfall simulations. Although the talus slope features are quite constant, an unexpected wide range of restitution coefficients results from the movies: the variability is greater than that one of bibliography, moreover normal restitution coefficients are extremely high (they often overpass the unit). The qualitative relationships between restitution coefficients and slope features, falling block characteristics and pre-impact motion conditions have been searched and described.