Fully coupled dynamic simulations of uncompacted railway embankments under train loading

Unlike modern earthworks, historic railway embankments were often end-tipped rather than compacted in layers and are susceptible to significant deformation and potentially failure. This study assesses the mechanical and hydraulic behaviour (deformation, stress migration and build-up of internal pore water pressure) of uncompacted railway embankments under different train loading conditions. A mixed finite-element approach based on the complete solid displacement, fluid displacement and pore pressure (u–w–pw) formulation incorporating a multiaxial cyclic mobility model was used to analyse the non-linear, transient response of the track–embankment–ground system. Analyses considered various loading scenarios from a single moving axle to trains of varying length and axle load on embankments of different hydraulic conductivity. Embankment hydraulic conductivity, axle load and train length were found to affect distributions of maximum and residual excess pore pressure and vertical displacement with depth in different ways. For example, longer trains passing at a given speed induce smaller residual excess pore pressures at shallower depths because of the increased time available for excess pore pressure dissipation, but greater residual pore pressures at greater depths, further from the drainage boundary, where the effects of loading can accumulate.