Flow and Pressure of Granular Materials in Silos

The internal flow behavior of a bed of granular material is described as discharge from model silos occurs. Results of experiments with various models suggest that fundamental flow patterns are associated with discharge. It is shown that the flow is essentially a steady-state phenomenon when viewed from a reference system external to the silo. Pressures far in excess of the static pressures computed by standard silo design techniques have resulted in many silo failures. The relation between the existence of these overpressures and the fundamental flow patterns is shown. An approximate upper bound plasticity solution to the pressures on the walls of silos is presented. This conservative upper bound predicts pressures from four to eight times the computed static pressure by taking the fundamental flow patterns into account. The overpressures are a steady state phenomenon and it is suggested that they be taken into account in silo designs.