Resumen de Rockfall analysis: failure, fragmentation and propagation characterization
The present thesis aims at the analysis of the fragmentation of rockfalls. The fragmentation is a complex phenomenon poorly understood with a lack of tools to reproduce it on rockfall simulators. The effect of fragmentation on the hazard assessment and mapping is significant and it may substantially modify the risk scenario. The analysis of the empirical data acquired in a series of inventoried natural rockfalls and real-scale drop tests, clearly suggests that fragmentation displays a fractal behavior. Based on these observations, a fractal fragmentation model is proposed heare, adapting the basics of Perfect (1997) to the specific case of rockfalls. An important development of the thesis presented is the procedure to characterize the rockfall mass before and after the fragmentation, which include the methodology to measure the block size distributions of the deposit, the use of Unmaned Aerial Vehicles (UAV) equipped with digital camera digital, and the photogrammetric analysis to reconstruct the detached block volumes based on 3D models and discrete joint characterization. The block size distributions before and after the fragmentation are related with the proposed model, using the real data to calibrate the model parameters by back analysis. The methodologies and the model proposed contribute to the understanding of the fragmentation phenomenon and have the capability to reproduce the entire block size distribution and the calculation of the number and volume of the fragments. They also allow the quantification of the areas of the fresh faces created due to breakage, which may be related to the required fragmentation energy. The final goal of the ongoing research is the implementation of fragmentation behavior on a rockfall simulator which is currently under developed within the Rockmodels project (https://rockmodels.upc.edu/es), and modify the criteria to calculate the probability of impact used in hazard mapping and in quantitative risk assessment studies. The results of the fragmentation model may also contribute to the analysis of the efficiency and to the design of the rockfall protection systems.
