Kinematic behavior of sheared sand with emphasis on particle to particle interaction using computed tomography

Granular materials are a three-phase mixture of solid, liquid, and gas that exhibit complex engineering properties. They have a heterogeneous composition in nature and consist of many discrete particles with complex interactions. Granular materials are commonly used in many civil engineering construction projects, therefore, a better understanding of behavior of granular materials may result in safe and economical design. This thesis is a compilation of two related topics. A 3D systematic experimental study that investigates the influence of particle morphology, confining pressure, and specimen density on the failure mode of sheared sand is presented. Three uniform sand specimens with different morphologies as well as spherical glass beads were tested under axisymmetric triaxial loading. The deformation of the tested specimens was monitored using in-situ 3D Synchrotron Microtomography (SMT), and maps of incremental particle translation and rotation were developed. The results of the analysis shows that the angularity of particles is the major player in the failure mode of the sheared sand under high confining pressure, where specimens fails either via a single well-defined shear band or via a bulging mode. Dense specimens tested under low confining pressure, as well as loose specimen exhibited a preference to fail via bulging in the middle of the specimens. The second part of the Thesis presents an experimental validation of the finite strain formulations that were developed by Zhang and Regueiro (2015) using 3D images of sheared F35 Ottawa sand specimens. The spatial maps of Eulerian octahedral shear strain were used to identify intensive shearing zones within the specimens, and compared well with maps of incremental particle translation and rotation for the same specimens. The local Eulerian volumetric strain was compared to the global measurements, which also can be considered v as an averaging of all local Eulerian volumetric strains. Void ratio evolution curves generally compared well with the volumetric strains at both the local and global level.