ABSTRACT
The vast majority of railway design engineers have regarded ballast as an elastic granular media. Various researchers have empirically modelled the permanent deformation of ballast under cyclic loading. This chapter discusses plasticity models that are expected to be useful in simulating the deformation and degradation of ballast under cyclic loading. Although the original critical state model was based on extensive laboratory test results of remoulded clay, some researchers attempted to model the deformation behaviour of sands and gravels similar to the critical state (Cam-clay) model. To realistically model the stress–strain behaviour of soils under cyclic loading, some researchers introduced the concept of bounding surface plasticity in their formulations. The simple elasto-plastic or non-linear elastic models may be used to simulate the deformation behaviour of soils under monotonic loading with sufficient accuracy. Some investigators attempted to quantify the degree of particle breakage, while others correlated the measured breakage indicator with various engineering properties of ballast and other granular aggregates.
