| Summary: | 碩士 === 國立臺灣工業技術學院 === 工程技術研究所 === 80 === Stress and void ratio are two very important factors affecting the mechanical behavior of sand. But, they alone can not fully characterize the anisotropy and dilatancy of sand. The effect of fabric must be taken into account.
This research investigated the behavior of sand and its fabric evolution under different stress paths, both experimentally and numerically. Cubic samples Ottawa sand were tested by a true triaxial testing device with different stress paths. During test, the stiffness of each direction and the dilatancy of the samples were measured. Numerical analysis was performed by a discrete element code, TRUBAL, to simulate the true triaxial test results. The suitability of the code could be verified by comparisons of the numerical results with the experimental ones. Then, the fabric evolution and its effect on the stiffness and dilatancy could be investigated numerically.
The experimental results indicated that the mechanical behavior of the reconstituted specimens were affected by the initially cross-anisotropic fabric and the changes of the intermediate principal stress direction. When the major principal stress acted parallel to the direction of specimen deposition the specimens had the largest initial stiffness and rate of dilation, but when the minor principal stress acted parallel to the direction of specimen deposition the specimens had the smallest initial stiffness and rate of dilation.
The numerical results indicated that the computer program TRUBAL with non-linear Hertz contact law could simulate the behavior of granular material both qualitatively and quantitatively, but the experimental samples contracted in the initial portion of shear which was not the case in the numerical results. Fabric evolution was investigated by numerical analysis. It was found that during shear deformation, the change of the fabric was behind the change of the stress but ahead that of the strain. When the shear stress returned to zero, the fabric still had more contact normals in the previous major principal stress direction. The initially cross-anisotropic fabric was also found to have influence on the subsequent fabric evolution. When resheared along the previous shearing direction the samples had the largest initial stiffness and rate of dilation, but when resheared opposite to the previous shearing direction the samples had the smallest initial stiffness and rate of dilation.
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