Granular compaction under confinement.

Successive vertical vibrations can cause a granular pack to rearrange and move to more and more dense configurations. The dilation of the pack that occurs during the vibrations is important to these rearrangements and the resulting compaction of the system. This paper presents an experimental study in which a confining force is used to limit the amount of dilation of the pack.

Behavior of granular materials under cyclic shear.

The design and development of a parallel plate shear cell for the study of large-scale shear flows in granular materials is presented. The parallel plate geometry allows for shear studies without the effects of curvature found in the more common Couette experiments. A system of independently movable slats creates a well with side walls that deform in response to the motions of grains within the pack.

Force distributions in three-dimensional compressible granular packs.

We present an experimental investigation of the probability distribution of normal contact forces, P(F), at the bottom boundary of static three-dimensional packings of compressible granular materials. We find that the degree of deformation of individual grains plays a large role in determining the form of this distribution. For small amounts of deformation we find a small peak in P(F) below the mean force with an exponential tail for forces larger than the mean force.

Stress transmission through three-dimensional ordered granular arrays.

We measure the local contact forces at both the top and bottom boundaries of three-dimensional face-centered-cubic and hexagonal-close-packed granular crystals in response to an external force applied to a small area at the top surface. Depending on the crystal structure, we find markedly different results which can be understood in terms of force balance considerations in the specific geometry of the crystal. Small amounts of disorder are found to create additional structure at both the top and bottom surfaces.

Force distributions in three-dimensional granular assemblies: effects of packing order and interparticle friction.

We present a systematic investigation of the distribution of normal forces at the boundaries of static packings of spheres. A method for the efficient construction of large hexagonal-close-packed crystals is introduced and used to study the effect of spatial ordering on the distribution of forces. Under uniaxial compression we find that the form for the probability distribution of normal forces between particles does not depend strongly on crystallinity or interparticle friction.