Abstract: The study of dynamic-hydraulic characteristics and fine particle migration of sand-silt mixtures under load is the basis and key for analyzing the mesoscopic disaster-causing mechanism and evolution mechanism of natural or engineering disasters such as vibration liquefaction and mud pumping etc. The experimental study on fine particles migration mechanism of saturated sand-silt mixtures under combined dynamic-static train load was carried out by using the self-developed test system. The experimental results show that the axial deformation of the sample exhibits a “stepped” change trend. The total stress distribution shows an exponential decrease with increasing depth. The pore water pressure in the sample experiences the cyclic process of accumulation under dynamic loading and dissipation under static loading. In this process, the axial gradient of pore water pressure gradually forms a "pumping" effect on pore water, which causes the migration of fine particles and water. Furthermore, by analyzing the composition change of three particle size groups contents and effective diameter d10 of different layers of the sample, it is analyzed the combined dynamic-static loads affect fine particle migration in saturated sand-silt mixtures.

Key words: cyclic loading, test system, sand-silt mixtures, fine particle migration, pore water pressure