Weakly cemented granular materials study at multiple length scales

Abstract

Cemented granular systems are encountered at various scales in nature and artificially. We present an experimental study carried out on the structure and mechanical behaviour of weakly cemented granular materials. We study the cemented granular materials at two scales -- micro (particle-bond-particle) scale and macro (ensemble) scale. At the micro-scale studies, a set of x-ray computed tomography experiments are performed. We characterize the structure of initial configuration of weakly cemented granular materials. We discuss, in detail, quantification of fabric and structure such as coordination number, fabric tensor, directional distribution of contact normal and particles, and grain size distribution. An alternative approach to arrive at the fabric tensor is also discussed. To obtain these characteristics, the scanned volume from XCT is segmented into particles and contacts (bonds - for a contact bound structure). For the segmentation, watershed along with h-minima or h-maxima transform are used. The algorithm is presented in detail for a two dimensional example image. From the segmentation results, it is observed that the particles of cemented granular materials orient themselves away from the direction of the gravity or body force whereas the contact normals have a tendency to orient along the direction of gravity. Further, we perform a set of uni-axial compression tests inside the X-ray computed tomograph. It is observed that the initial structure of cemented granular material does not changes significantly before the peak load is reached. The average coordination number increases at lower strains due to contraction of the specimen however at larger strains, continuous reduction in coordination number is observed. The evolution of average porosity field has similar trend to the volumetric strain. Further, the particle and contact align themselves along the direction of load at lower strains whereas at higher strains, they orient themselves away from the loading direction. At macro-scale, we perform a set...