Research on Pumping Effect in Base-Course or Subgrade on Rutting Behavior of Asphalt Pavements

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The objective of this research is to establish the analytical technique for the sudden increase in rutting behavior after the occurrence of surface layr cracks, from the viewpoint of the pumping phenomenon of the base layr or the subgrade. Major information obtained from each experiment and analysis in this research are listed below :1. Repeated plate loading tests using the small scale model test equipment manufactured : For both crushed aggregate as base material and masado as subgrade material, the settlements of the saturated state under plate loading were 2 to 4 times bigger than those of the wet state, depending on the testing conditions. For only the base material, confirmed as the causes for this were the development of the pumping phenomenon and its area of development.2. Materials characterization tests using the existing repeated triaxial test equipment : The resilient and permanent deformation characteristics of the saturated state and the wet state did not show any remarkable differences. Materials characterization, therefore, assuming to correspond to those whose soil elements within the pumping area had already reached static failure, were attempted. The results were approximately similar to the characteristics of loose state materials.3. Analysis of repeated plate loading test's results : The analytical results using the iterative finite element method of the wet state were comparatively good but the results of the saturated state were slightly lower than the experimental results. This is thought to be due to the small size of the loading plate which are unstable, the disregard of the increase in the specimen deformation until it reached static failure, etc.4. Rutting analysis of test pavements : In spite of the inadequacy of the analytical results explained above, the application of the above analytical technique to test pavements showed good results. This suggests the complexities of the in-situ pavement conditions.