Evolution of structure of cohesive granular ensembles in compression

A small amount of cementation between particles drastically changes the mechanical response of a granular ensemble. Through a series of interrupted uniaxial compression tests inside the x-ray computed tomograph (XCT) on fine and coarse grained cemented sand specimens, a quantification of the behavior at both the continuum and particle scales is made. At the continuum length scale, displacements and porosity fields are examined. While at the particle scale, the coordination number, particle and contact fabric tensors, directional distribution of particles and contact normals are extracted and analyzed. Particle level phenomenology—at different stages of loading—such as breakage of bonds, formation of new contacts, manifest themselves at the ensemble scale in the form of bifurcation zones, which coalesce into split zones through the specimen. A new paradigm for the fabric tensor is also provided using principal component analysis. The results of the continuum and particle scale analysis are used to provide insights on the compression behavior of cemented sands.