Field Evidence and Kinematical Back-Analysis of Block Rebounds: The Lavone Rockfall, Northern Italy

This paper reports the field evidence and the kinematical study of the motion of two blocks (A and B) mobilised by a rockfall in Lavone (Valtrompia, northern Italy) on 14th February 1987. The two sequences of impact marks left by the blocks on the ground surface were measured and the lithostratigraphical features of the debris slope were surveyed. On the basis of the field-collected input data, several computer simulations were carried out to calculate the coefficients of restitution (E) satisfying the trajectory conditions. The computed output values, obtained by running a specific automatic program for rockfall modelling, show that rebound trajectories require high coefficients of restitution (0.8 ≤ E ≤ 0.9). Back-calculated impact velocities range from 9.2 to 19.8 m/s. Trajectory heights vary from 0 to 2.4 m above the slope surface. Block trajectories differ considerably according to the circumstances of initial air projection, i.e. to the initial rebound angle (α _r). The calculated values of α _r denote a considerable range (36°), emphasising the high variability and the random nature of this parameter. The described case history shows that rockfall computer analyses can be an effective tool to describe the bouncing propagation of single blocks, but care must be taken in choosing the restitution coefficient E and the geometrical parameters of initial air projections.