Development of Element tests for elucidating mechanical behavior of granular materials subjected to cyclic moving loads

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This study examines the mechanical behavior of granular materials subjected to cyclic moving loads, for example gravel roadbed and railroad ballast, and both a new testing method and new analytical procedures to examine the effects of the rotation of principal stress axes on cyclic plastic deformation of granular materials are proposed. The following conclusions can be obtained ;1.Cyclic plastic deformation obtained through moving loading tests is much larger than those obtained through fixed-place cyclic loading tests when other experimental conditions are the same. Accordingly, the difference in loading methods has a significant influence on the cyclic plastic deformation of granular materials.2.Residual strain obtained through cyclic loading triaxial tests with constant amplitude of deviator stress while controlling confining pressure constant is very small compared with the macro residual strain calculated from force-displacement relationships in moving loading tests, while that of … More cyclic torsional simple shear tests using a newly developed "Multi-ring shear apparatus" is almost equivalent to moving loading tests. Therefore, the multi-ring shear test is appropriate for an element test to simulate the actual stress states inside substructures under traffic loads. Moreover, it was revealed that the rotation of principal stress axes has a significant effect on cyclic deformation characteristics of granular materials.3.Two analytical procedures for simulating the mechanical behavior of granular materials subjected to cyclic moving loads were proposed. One is linear elastic FE analysis considering the material properties of cumulative strain derived from element test results of granular materials, which can roughly estimate the residual settlement of granular substructures due to cyclic loading. The other is discontinuous analysis which elements imitate the shape of real gram particles well because it was revealed that the element shape is one of the dominant factors to determine the mechanical behavior of granular assemblage in discontinuous analysis. Less