Abstrakt

Shear zones are a fundamental phenomenon associated with the deformation of granular materials. Under significant load, these materials develop zones of plasticity concentrated in a narrow layer, characterized by a substantial increase in deformation and frictional resistance between the grains. The main objective of this doctoral thesis was to investigate the formation of shear zones in a cohesionless granular material (sand) at the grain-level using the Discrete Element Method (DEM) during silo flow in a laboratory-scale setup. The numerical model of the sand consisted of discrete particles with diameters enabling the analysis of shear zones at the mesoscale level. This approach allowed for detailed studies of the shear localizations and its impact on silo structures. In the first part of the work, the numerical model was calibrated based on experimental studies available in the literature, such as tests in a triaxial compression apparatus and a direct shear apparatus. The calculations considered various initial densities, different load applied to the samples, and different surface geometries (e.g., their roughness) in the case of interface studies. The calibration tests focused on examining the shear zone at the boundary between the granular material and structures with varying geometries. Another part of the thesis involved experimental studies of shear zones at the contact area between sand and a sinusoidal corrugated surface using the direct shear apparatus. The Digital Image Correlation (DIC) method was used in the experiments. In the second part of the work, the numerical results of quasi-static and gravitational flows in laboratory-scale silos were presented. The analysis examined the sand structure at the grain-level, determining distributions of such characteristics as grain displacements, grain rotations, voids between grains, contact force chains, and internal stresses within the material. The DEM results were directly compared with experimental results available in the literature. The flow studies considered various initial densities of the granular material, different silo wall roughness, and different locations and sizes of the silo discharge outlet. A good agreement was obtained between the discrete model and the experiments, both in terms of the forces acting on the silo structure and the propagation of shear zones in the granular material.

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