Impact of rocks onto gravel Design and evaluation of experiments

Layers of gravel represent an energy-absorbing system for structures subjected to rockfall. To support the design of such structures, relations between the penetration depth, the impact duration, and the impact force, respectively, and the rock boulder mass, the height of fall, and the indentation resistance of the gravel are presented. Knowledge about projectiles impacting onto concrete and soil is incorporated in these relations. They can be simplified by dimensional analysis. This is the basis for the design of rockfall experiments comprising heights of fall up to 20 m , and a rock boulder mass up to 20 000 kg . From these experiments, the indentation resistance of gravel is obtained by back-analysis and evaluated statistically. This permits estimation of penetration depths caused by rockfall events which are beyond the experimental means of the current study. Finally, a model for the impact kinematics is deduced from experimental acceleration measurements. It yields design diagrams for impact duration and impact forces, supporting probability-based engineering design of rockfall protection systems with gravel as an energy-absorbing component.