Inclined Block Impacts on Granular Strata: Coupled DEM-FDM Numerical Investigation and Rheological Modelling.

In mountain regions, rockfall is a very widespread natural hazard, difficult to be numerically simulated, from the initial detachment of the block to its impact on natural/artificial strata. When a rock block impacts on a granular stratum, the interaction is dominated by inertial effects and is severely affected by block mass, shape, velocity magnitude/direction, and soil geomechanical properties. The kinematic description of the response of the block during the impact requires complex and time-consuming numerical modeling approaches. Moreover, these numerical approaches cannot be easily coupled with classical mass-lumped rockfall analysis tools employed to simulate blocks trajectory. To overcome this problem, a dynamic upscaled visco-plastic rheological model (BIMPAM), suitable for simulating inclined impacts on generally inclined deformable strata, has been conceived in the past by one of the authors. Up to now, due to the absence of suitable numerical and experimental data, BIMPAM has been only validated on experimental large-scale vertical impacts on horizontal strata. In this paper, the impact problem is analyzed, by performing numerical analyses by means of a coupled Discrete Element and Finite Difference numerical model (DEM-FDM), calibrated on available experimental data, to provide (i) a novel numerical dataset highlighting the crucial role played by the impacting velocity inclination on the dynamic interaction between soil stratum and penetrating rigid object and (ii) a detailed micromechanical description identifying the processes responsible for the complex macroscopic behavior. The obtained numerical results have allowed to both validate BIMPAM model, even in case of inclined velocities, and provide a micromechanical interpretation of its constitutive assumptions. Highlights: The obtained numerical DEM-FDM results have allowed the authors to discuss how the initial velocity inclination affects impact kinematics. An upscaled constitutive relationship (BIMPAM model), previously conceived, has been validated for any impact inclination using the novel dataset obtained in the current work. The problem of DEM-FDM data reliability has been critically tackled proposing an original procedure for the generation/calibration of the coupled DEM-FDM model. The role of grain damaging, when the impact energy is sufficiently large, has been highlighted, from the direct comparison with large scale experimental test results. [ABSTRACT FROM AUTHOR]