Elastoplastic deformation behavior for ballast under monotonic and cyclic loading conditions

Various constitutive models for soils and gravels have been developed in the last century. Among them unconventional plasticity theory is a key and necessary approach for describing cyclic deformation behavior of materials. The "subloading surface model" proposed by Hashiguchi, which belongs to the unconventional plasticity framework, does not assume a purely-elastic domain inside a yield surface and premises that an inelastic strain is induced by stress changes inside the yield surface. It is able to describe the mechanical behavior of materials such as not only smooth elastoplastic transition but also cyclic loading behavior. Thus, elastoplastic constitutive models for various materials based on this model have been developed up to present. Moreover computational analysis methods such as a finite element method (FEM) incorporating this constitutive model have been utilized for solving problems in geotechnical engineering fields. On the other hand, gravel such as ballast causes elastoplastic deformation in the proportional loading process. However the accumulation of the plastic deformation under a cyclic loading condition is smaller than that for typical soils such as sand and clay in general since the elastic property of ballast particle is high and the slip between each ballast is remarkably suppressed by the particles' packing. In this study, the subloading surface model is modified by assuming an existence of the elastic domain surface inside the subloading surface so as to realistically describe the inelastic deformation behavior of ballast including monotonic and cyclic loading conditions. The validity of the model is verified by the comparison with large-scale triaxial compression test data for both loading conditions.