Macro-microscopic dynamic characteristics of the ballast bed induced by the variation of moisture content

Abstract

Due to the excellent drainage performance of the ballast, existing studies mainly focus on the dynamic response of ballast under field capacity or saturation. Attention has rarely been paid to dynamic changes in moisture content and potential influences. In this article, we firstly conduct a model test to determine the variation of ballast moisture content under artificial rainfall. After that, a full-scale model test with cyclic loading is carried out to study the effect of moisture content variation on the macro-microscopic response of the ballast bed, where several wireless particle sensors are installed to obtain ballast motion characteristics at strategic locations. The results show that the moisture content increases gradually and stabilizes at a flat peak under rainfall, despite the excellent drainage performance of ballast bed. After halting rainfall, the moisture content drops back to field capacity, which indicates dynamic flowing surface water on ballast particles under rainfall. Such flowing surface water brings changes to the original dynamic equilibrium of ballast bed: macroscopically, the deformation rate of stabilized ballast bed increases significantly, reaching a local peak under field capacity; microscopically, the x- and z-angular accelerations of the ballast show positive correlation with rainfall intensity. The multiscale responses indicate that field capacity is a critical moisture content.