Upward migration of soil particles induced by the sloshing of slurries under cyclic load: experiments and theoretical explanation

Internal stability of subgrade soil under dynamic train loads plays an essential role in the serviceability of rail embankments. “Mud pumping”, the upward migration of fine particles and water from the subgrade, has been observed more often due to the increase of axle load and train speed. This paper presents a series of laboratory experiments to simulate mud pumping in rail embankments and provides a theoretical explanation. The test results show that the sloshing of slurries within a layered gravel-silt column under dynamic load causes the oscillation of excess pore pressure. The increase of turbidity will increase the sloshing damping of the slurry, thus causing the oscillation amplitude of excess pore pressure to decrease. A theory is proposed based on the dynamics of liquid sloshing, which confirms that the pressure gradient caused by slurry sloshing changes the seepage velocity in the subgrade soil, thereby providing the necessary hydrodynamic force for detachment and migration of fine particles. The relationship between the pressure gradient and loading frequency is acquired in numerical models and experiments. The engineering implications of this theoretical explanation are also discussed, in the context of designing reasonable train speed.