Abstract: The subgrade mud pumping of heavy-haul railway is widespread and harmful, which seriously affects the stability of tracks and the safety of train operation. The properties of railway subgrade soil, such as the particle size distribution, the void ratio, have a significant impact on the characteristics of subgrade mud pumping under the train load. In this study, a series of remolded samples consisted of silty clay and different contents of kaolin was subjected to mud pumping tests with a self-developed test model, and the influences of different particle size distribution (kaolin content) and different initial dry densities (void ratios) on the characteristics of axial strain, excess pore water pressure and fine particles migration under dynamic load were analyzed. The results show that with the increase in kaolin content and initial dry density, the axial strain and the excess pore water pressure of the samples, the average migration height of fine particles, and the degree of subgrade mud pumping all decrease. We also find that the excess pore water pressure gradient is the leading factor driving the migration of fine particles in subgrade soil, and the interlayer has a promoting effect on the occurrence of subgrade mud pumping.

Key words: mud pumping, particle size distribution, initial dry density, axial strain, excess pore water pressure, fine particles migration