Extending the Boussinesq model for impacts in granular media

Granular impact phenomena have implications in many areas. A fundamental problem deals with the mechanical response of a granular medium under external loads, such as those derived from the impact of a rigid object on the top of the medium. Here, the load changes its magnitude and intensity during the impact, being also applied in much shorter intervals than those of a static load, where the Boussinesq model is usually valid. This dynamic has been poorly addressed in the literature, a void to which this study aims to contribute, where we measure the pressure distribution transmitted at the bottom of a uniform, dry granular layer under the action of gravitational impacts of a steel sphere of fixed diameter. Exploring different bed thicknesses and drop heights, it is found that the structure of this distribution follows a similar form to the Boussinesq model, which was proposed initially for static conditions. This surprising result opens up several questions and future research challenges that could help validate or refute this model in other scenarios.