ABSTRACT
Ballast contamination or fouling combined with subgrade softening due to mud pumping is a significant issue faced by railways worldwide. When soft subgrade experiences cyclic loading, excess pore pressure and vertical deformation will continue to develop as the number of cycles increase; these actions will reduce the bearing capacity of the subgrade and lead to excessive settlement. The state of stress in an element of soil is generally defined in terms of the normal and shear stresses applied at the boundaries, which can be represented in a Mohr circle. There are two main types of drainage conditions that can be used to determine the shear strength parameters, i.e., drained and undrained conditions. When using the results of these laboratory tests to analyse the behaviour of geomaterials used in construction, the main consideration is the ratio between the rate at which the changes in total stress and the dissipation of pore water pressure occur.
