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.