Collapse dynamics and runout of dense granular materials in a fluid.

We investigate the effect of an ambient fluid on the dynamics of collapse and spread of a granular column simulated by means of the contact dynamics method interfaced with computational fluid dynamics. The runout distance is found to increase as a power law with the aspect ratio of the column, and, surprisingly, for a given aspect ratio and packing fraction, it may be similar in the grain-inertial and fluid-inertial regimes but with considerably longer duration in the latter case. We show that the effect of fluid in viscous and fluid-inertial regimes is to both reduce the kinetic energy during collapse and enhance the flow by lubrication during spread.

Tensile strength and fracture of cemented granular aggregates.

Cemented granular aggregates include a broad class of geomaterials such as sedimentary rocks and some biomaterials such as the wheat endosperm. We present a 3D lattice element method for the simulation of such materials, modeled as a jammed assembly of particles bound together by a matrix partially filling the interstitial space. From extensive simulation data, we analyze the mechanical properties of aggregates subjected to tensile loading as a function of matrix volume fraction and particle-matrix adhesion.

Subparticle stress fields in granular solids.

We rely on the lattice element method to simulate and analyze the stress fields at subparticle scales in two-dimensional granular solids composed of particles of variable stiffness together with an interstitial matrix of variable volume fraction. We find that the contact force distributions as approached from the subscale stresses are similar to those obtained from a particle-scale discrete element approach. This means that the well-known properties of force distributions in model granular media, with hard particles and without an interstitial phase, can be extended to materials such as concrete and sandstone involving a jammed particle phase.

Strength and failure of cemented granular matter.

Cemented granular materials (CGMs) consist of densely packed solid particles and a pore-filling solid matrix sticking to the particles. We use a sub-particle lattice discretization method to investigate the particle-scale origins of strength and failure properties of CGMs. We show that jamming of the particles leads to highly inhomogeneous stress fields.