A semi-empirical impact force model of irregular rockfall on granular layer and its experimental validation

Rockfalls can pose a significant threat to traffic safety in mountainous areas. Galleries covered by a granular layer have proven effective in protecting both the people and the infrastructure from falling rock blocks. However, quantifying the impact for structural design purposes remains challenging as this force is strongly influenced by the shape of the blocks, among other factors. Here, we propose a semi-empirical model to evaluate the maximum value of the impact force exerted by an irregularly-shaped rock block on a granular layer. The model introduces a work-energy ratio (& alpha;), which is a dimensionless parameter that depends on properties of both the block and the granular layer. We evaluate a significant dependence of & alpha; on the block shape (N*) as well as on the thickness (Ts) and strength-like indentation resistance (f*) of the granular layer. We show that & alpha; is lower for blocks with sharp noses (low N*) and for layers with low f*. Furthermore, we identify a threshold value of Ts, above which & alpha; becomes independent of Ts. We validate our model on large-scale experiments as well as on a variety of published data and compare the model's performance with that of existing models. The model exhibits superior performance in realistic rockfall scenarios, suggesting a good potential for implementation in gallery design.