Steady state response of a granular layer to a moving load - a discrete model

This paper discusses the steady state response of a rigidly supported, granular layer to a moving load. Accordingly, the dynamic behaviour of a ballast layer under an instantaneous train axle passage is simulated, where the rigid support reflects a substratum that is much stiffer than the ballast layer, e.g. ballast in a concrete railway tunnel or on a concrete railway foundation. The discrete nature of the layer is captured via a 9-cell square lattice. After deriving the equations of motion for the lattice, the long-wave approximation of the equations of motion is compared with the equations of motion for a continuum model. This leads to relations between the macroscopic constitutive parameters of the continuum and the microscopic constitutive parameters of the discrete lattice. Next, the boundary value problem is formulated and solved. The influence by the particle size, the damping characteristics and the load velocity on the layer response is demonstrated via a parametric study