Study on Elucidation and Prediction of Mechanical Behavior of Saturated/Unsaturated Granular Base Subjected to Cyclic Moving Loads.

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This study examines the mechanical behavior of granular materials under saturated and unsaturated conditions subjected to cyclic moving loads, for example gravel roadbed and railroad ballast, and both a new testing methods and new analytical procedure to examine the effects of the rotation of principal stress axes and water content on cyclic plastic deformation of granular base course materials are proposed. The following conclusions can be obtained;1. Two types of small scale model tests which adopted a fixed-place loading method and a moving loading method were performed with a base course material under air-dried condition and saturated condition. As the results, it was revealed that the water content of the base course material influences the mechanical behavior of granular base strongly, and the effect on the development of residual settlement for granular base under cyclic loading remarkably comes to the surface in employing moving loads.2. Two types of multi-ring shear tests, which can consider a change in direction of principal stresses like traffic loads, were performed in the same way as loading methods in small scale model tests. As the results, it was revealed that the shear strength decreased and the cumulative residual strain increased due to the saturation, and that the mechanical behavior in multi-ring shear tests is very similar to that in small scale model tests, regardless of loading methods and water contents.3. A new method to estimate cyclic plastic deformation of granular base under repeated wheel traveling in terms of the strength and deformation characteristics of granular base course materials was proposed. The simple analytical procedure with linear elastic FE analysis considering the cumulative strain derived from multi-ring shear test results of base course materials can roughly estimate the residual settlement of granular base under saturated and unsaturated conditions subjected to cyclic moving loads.