Study on characteristics and mechanism of subgrade mud pumping under heavy-haul train loads

Subgrade mud pumping is a worldwide problem that seriously threatens railway track stability and operational safety. This paper analyzes the influence of Kaolin content (plasticity index) on the characteristics of saturated subgrade mud pumping under cyclic loading using a self-developed test model. Test samples consist of clay mixed with 10%, 20%, and 30% of Kaolin. The results show that the addition of Kaolin can reduce the void ratio (for a given initial dry density) and create a more plastic soil which is less prone to fluidisation under loading, thus reducing the axial strain and excess pore water pressure which helps to mitigate the problem of mud pumping. Based on our test results, we put forward a criterion to distinguish whether mud pumping occurs. In addition, we find that the excess pore water pressure gradient in subgrade soil plays a key role in the migration of fine particles and that the generation of an interlayer under cyclic loading can also promote subgrade mud pumping.