| The objective of this dissertation is to develop a ballast quality evaluation computer model based on the relations among the ballast particle characteristics and ballast performance.; Much effort has been given in the past to seek suitable criteria for ballast material selection considering ballast performance and maintenance costs. But the selection of ballast material has appeared to be based on limited information without full regard to the effect of ballast particle characteristics on the ability of ballast to fulfill its functions in track. This will result in some misjudgments in the ballast material selection.; The developed model can quantify the ballast suitability with a ballast quality index which has taken the basic ballast particle characteristics and the main ballast field functions into consideration. The basic ballast particle characteristics included are shape, angularity, surface texture, gradation, and specific gravity. The main ballast field functions for track are providing resistance forces, resiliency, void storage, drainage, and facilitating maintenance. The ballast particle characteristics are numerically related to the ballast field functions based on available data from field and laboratory tests on granular materials and some assumptions. Weighting factors are used to represent the relative importance of the basic ballast particle characteristics to each ballast function and then the relative importance of the main ballast functions to the overall ballast field performance.; The developed model is evaluated using the ballast field data related to the track performance. The verification results show that the developed ballast quality index can reflect the ballast quality. |
