| Summary: | 碩士 === 國立成功大學 === 土木工程學系碩博士班 === 101 === This study aims to investigate the size and boundary effects in direct simple shear test with Distinct Element Method (DEM), and clarify the relation between the maximum particle size and the specimen size for element test on soils with large particles. The numerical procedure was verified with results from triaxial models and corresponding laboratory triaxial test using uniform steel balls. To evaluate the boundary effect, spatial variations of stress and strain within the specimen is studied for different height and diameter ratios (H/W) and two types of direct simple shear apparatus. The purpose of the size effect, is to determine the relation between the maximum particle size and specimen size for consistent shearing responses. The result shows that : (1)the boundary effect can be reduced effectively when H/W decreases, (2)the difference in boundary effect is insignificant between the Cambridge and NGI types of simple shear, (3)a relatively constant strength is available when the ratio of specimen height to the maximum particle size (H/dmax) is no less than 7 ; otherwise the shear strength is significantly influenced with the maximum particle size, and (4)DEM can simulate the rotation of principle stress during simple shear shearing process.
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