Negative grain-pressures in frictional cohesionless granular media with elongated particles

By subjecting a granular assembly to confining pressure, it is expected that each particle is compressed (positive pressure). This study highlights a situation where some particles find a mechanism to find themselves in tension (negative pressure), while the sample is compressed. This state is achieved by packing elongated rod-shaped particles in a cylindrical box and applying an uniaxial compression. Using discrete element simulations with the code Rockable, able to model sphero-polyhedral shapes, an analysis is conducted to characterize this striking feature at first glance. The particle length are varied to show at which elongation ratio the long range interactions become sufficient to allow for friction to pull the particles, i.e. , make the negative grain-pressures emerge. A relation linking the orientations of negative grain-pressures to the loading direction is presented through statistiscal analyses.