Stress-dilatancy behaviour of fouled ballast: experiments and DEM modelling

This paper presents a study of the mechanical behaviour of ballast contaminated by different fouling agents such as coal and subgrade clay. Large-scale direct shear tests were carried out to examine the strength and deformation properties for coal-fouled and clay-fouled ballast. The experimental results show that fouled ballast (both clay and coal) exhibits a lower peak shear strength and decreased dilation during shearing. The clay-fouled ballast shows higher shear strength and smaller dilation compared to coal-fouled ballast. The relationship between shear stress and dilatancy of ballast under different fouling conditions is reported in this paper, where the numerical predictions are made using the discrete element method (DEM). The DEM simulations show that with the increase of fouling level, the coordination number, the average contact force, the particle rotation and the velocity decrease for ballast aggregates. The results indicate that coal-fouled ballast exhibits a smaller average contact forces with less stress concentrations, less major principal stress orientation and a greater coordination number, leading to less particle rotation and velocity compared to those of clay-fouled ballast for the same degree of fouling. Graphic abstract