Explosion cratering in 3D granular media

Sudden release of energy in an explosion creates craters in granular media. In comparison with well-studied impact cratering in granular media, our understanding of explosion cratering is still primitive. Here, we study low-energy lab-scale explosion cratering in 3D granular media using controlled pulses of pressurized air. We identify four regimes of explosion cratering at different burial depths, which are associated with distinct explosion dynamics and result in different crater morphologies. We propose a general relation between the dynamics of granular flows and the surface structures of the resulting craters. Moreover, we measure the diameter of explosion craters as a function of explosion pressure, duration and burial depth. We find that the size of the craters is non-monotonic with increasing burial depth, reaching a maximum at an intermediate burial depth. In addition, the crater diameter shows a weak dependence on explosion pressure and duration at small burial depths. We construct a simple model to explain this finding. Finally, we explore the scaling relations of the size of explosion craters. Despite the huge difference in energy scales, we find that the diameter of explosion craters in our experiments follows the same cube root energy scaling as explosion cratering at high energies. We also discuss the dependence of rescaled crater sizes on the inertial number of granular flows. These results shed light on the rich dynamics of 3D explosion cratering and provide new insights into the general physical principles governing granular cratering processes.