ABSTRACT
Ballast and subballast are two layers of non-cohesive, granular materials with different grain sizes filled in the track substructure to bear traffic loadings due to train passages. The performance and sustainability of a track substructure depend on both of these two granular layers. This paper presents the experimental results of cyclic triaxial testing on individual ballast and subballast materials. Besides, to investigate mechanical behavior at ballast/subballast interface, cyclic testings were performed on composite specimens consisting of the upper half ballast layer and underlying half subballast layer. These cyclic tests indicated that existence of ballast/subballast interface depresses the development of permanent axial or volumetric deformation at the interface zone, and this effect vanishes as the initial compaction and confining pressure increase.
