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We report on an experimental investigation of craters generated by explosions at the surface of a model granular bed. Following the initial blast, a pressure wave propagates through the bed, producing high-speed ejecta of grains and ultimately a crater. We analyzed the crater morphology in the context of large-scale explosions and other cratering processes. The process was analyzed in the context of large-scale explosions, and the crater morphology was compared with those resulting from other cratering processes in the same energy range. From this comparison, we deduce that craters formed through different mechanisms can exhibit fine surface features depending on their origin, at least at the laboratory scale. Moreover, unlike laboratory-scale craters produced by the impact of dense spheres, the diameter and depth do not follow a 1/4-power-law scaling with energy, rather the exponent observed herein is approximately 0.30, as has also been found in large-scale events. Regarding the ejecta curtain of grains, its expansion obeys the same time dependence followed by shock waves produced by underground explosions. Finally, from experiments in a two-dimensional system, the early cavity growth is analyzed and compared to a recent study on explosions at the surface of water. [ABSTRACT FROM AUTHOR]

An intruder penetrating into a granular column experiences a depth-dependent friction force F(z). Different regimes of F(z) have been measured depending on the experimental design: a nearly linear dependence for shallow penetrations, total saturation at large depths, and an exponential increase when the intruder approaches the bottom of the granular bed. We report here an experiment that allows us to measure the different regimes in a single run during the quasistatic descent of a sphere in a light granular medium. From the analysis of the resistance in the saturation zone, it was found that F(z) follows a cube-power-law dependence on the intruder diameter and an exponential increase with the packing fraction of the bed. Moreover, we determine the critical mass mc required to observe infinite penetration and its dependence on the above parameters. Finally, we use our results to estimate the final penetration depth reached by intruders of masses m

When rough grains in loose packing conditions are discharged from a silo, a conical depression with a single slope is formed at the surface. We observed that the increase of volume fraction generates a more complex depression, characterized by two angles of discharge: one at the bottom similar to the angle of repose and a considerably larger upper angle. The change in slope appears at the boundary between a dense stagnant region at the periphery and the central flowing channel formed over the aperture. Since the material in the latter zone is always fluidized, the flow rate is unaffected by the initial packing of the bed. On the other hand, the contrast between both angles is markedly smaller when smooth particles of the same size and density are used, which reveals that high packing fraction and friction must combine to produce the observed geometry. Our results show that the surface profile helps to identify by simple visual inspection the packing conditions of a granular bed, being useful to prevent undesirable collapses during silo discharge in industry. [ABSTRACT FROM AUTHOR]