Pumping effect of rainfall-induced excess pore pressure on particle migration

Abstract

Mud pumping in rail embankments has been observed in rainy seasons. In this study, a layered gravel-silt column was tested under cyclic loading to investigate the mud pumping mechanism caused by rainfall. The results show that liquid sloshing is more violent (larger velocity and wave height) with the water level higher. The pumping effect of sloshing-induced excess pore pressure leads to seepage in the sandy silt, and this seepage causes fine particles to detach from the skeleton particle surface. The size composition of migrating particles includes three orders of magnitude, which challenges the reliability of current numerical simulations in mud pumping. The uplift force and drag force of particles gradually increase as the water level rises, and the effects of uplift force on particle detachment exceed that of drag force. The evolution of slurry turbidity indicates that there is a water level threshold in the gravel layer, and a water level above the threshold will significantly promote the rate and extent of particle migration. The stability of particles under the pumping effect depends on the difference between hydrodynamic force and resistance. The findings from this study can help understand the engineering implications of waterproof and drainage systems in rail embankments to prevent the pumping effect.