Abstract: The foundation structure has a significant influence on the evolution of piping. A series of experiments on three typical foundation structures are carried out to investigate the process and mechanism of piping using a self-designed apparatus. The results indicate that a thin layer of cohesionless silty sand paved on the surface of the sandy gravel layer reduces the discharge in the outlet before erosion, meanwhile the critical hydraulic gradient is low and the developing speed of the piping channel is very fast. The piping mechanism in this foundation structure is different from that in two-stratum dike foundation. When the silty sand is laid at the certain depth of the sandy gravel layer, the critical hydraulic gradient increases greatly. Once the foundation is eroded, the erosion mass and the erosion rate will be very large, and the channel will be deep. The foundation will burst for the development of the channel if no effective measures are taken.