Abstract

This chapter focuses on packings and forces in dense non-cohesive granular materials. To maintain such a material in a steady static state requires the application of stresses at the boundaries. The forces and torques on each grain must add up to zero, and this condition (plus Newton’s third law) results in forces being sustained across a material. Equivalently, in the absence of body forces, the divergence of the stress tensor must vanish. This effect has sometimes been referred to as “propagation,” but it refers to a static, not dynamic, property. This is a strong mechanical constraint, and the way in which this constraint is satisfied for random packings is still at best a partially resolved issue. This chapter reviews some of the models and experiments that touch on this question; the interested reader can also find useful material in several reviews [1,2].