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Recent research showed that fracture of sand particles plays a significant role in determining the plastic bulk volumetric changes of granular materials under different loading conditions. One of the major tools used to better understand the influence of particle fracture on the behavior of granular materials is discrete-element modeling (DEM). This paper employed the bonded block model (BBM) to simulate the fracture behavior of sand. Each sand particle is modeled as an agglomerate of rigid blocks bonded at their contacts using the linear-parallel contact model, which can transmit both moment and force. DEM simulated particles closely matched the actual three-dimensional (3D) shape of sand particles acquired using high-resolution 3D synchrotron microcomputed tomography (SMT). Results from unconfined one-dimensional (1D) compression of a single synthetic silica cube were used to calibrate the model parameters. Particle fracture was investigated for specimens composed of three sand particles that were loaded under confined 1D compression. Breakage energy measured from DEM models matched well with that measured experimentally. The paper studied the effects of contact loading condition and particle interaction on the fracture mode of particles using BBM that can closely capture the 3D shape of real sand particles.

Tortuosity has a significant impact on flow and transport characteristics of porous media and plays a major role in many applications such as enhanced oil recovery, contaminant transport in aquifers, and fuel cells. Most analytical and theoretical models for determining tortuosity have been developed for ideal systems with assumptions that might not be representative of natural porous media. In this paper, geometric tortuosity was directly determined from three-dimensional (3D) tomography images of natural unconsolidated sand packs with a wide range of porosity, saturation, grain size distribution, and morphology. One hundred and thirty natural unconsolidated sand packs were imaged using 3D monochromatic and pink-beam synchrotron microcomputed tomography imaging. Geometric tortuosity was directly determined from the 3D images using the centroids of the connected paths in the flow direction of the media, and multivariate nonlinear regression analysis was adopted to develop a simple practical model to predict tortuosity of variably saturated natural unconsolidated porous media. Wetting phase saturation was found to provide a good estimate of relative tortuosity with an 2 value of .93, even with a porosity variation between 0.3 and 0.5 of the porous media systems. The proposed regression model was compared to theoretical and analytical models available in the literature and was found to provide better estimates of geometric tortuosity with an 2 value of .9 and a RMSE value of 0.117. INTRODUCTIONFluid transport in porous media can be encountered in a wide range of applications, including enhanced oil recovery, groundwater flow, contaminant transport in aquifers, geological storage of CO 2 , fuel cells, and batteries. Tortu-

Rock salt caverns have been extensively used as reliable repositories for hazardous waste such as nuclear waste, oil or compressed gases. Undisturbed rock salt deposits in nature are usually impermeable and have very low porosity. However, rock salt formations under excavation stresses can develop crack networks, which increase their porosities; and in the case of a connected crack network within the media, rock salt may become permeable. Although the relationship between the permeability of rock salt and the applied stresses has been reported in the literature, a microscopic study that investigates the properties influencing this relationship, such as the evolution of texture and internal stresses, has yet to be conducted. This study employs in situ 3D synchrotron micro-computed tomography and 3D X-ray diffraction (3DXRD) on two small-scale polycrystalline rock salt specimens to investigate the evolution of the texture and internal stresses within the specimens. The 3DXRD technique measures the 3D crystal structure and lattice strains within rock salt grains. The specimens were prepared under 1D compression conditions and have shown an initial {111} preferred texture, a dominant {110}〈110〉 slip system and no fully connected crack network. The {111} preferred texture under the unconfined compression experiment became stronger, while the {111}〈110〉 slip system became more prominent. The specimens did not have a fully connected crack network until applied axial stresses reached about 30 MPa, at a point where the impermeability of the material becomes compromised due to the development of multiple major cracks.