Abstract: Different foundation structure has different types of embankment piping. Previous researches have always focused on two-stratum dike foundation. In fact, the buried depth of fine sand has a significant influence on the piping development of foundations with fine sand. A series of simulated experiments is carried out to study the development process and mechanism of three-stratum dike foundations when the buried depth of fine sand changes. The results of experiments indicate that the burial depth of fine sand has a critical value. When the burial depth of fine sand is small, the critical hydraulic gradient is low and it’s easy to cause piping. After the occurrence of piping, more sand pours out of the embankment, and it leads to faster erosion. The critical hydraulic gradient increases as the buried depth of fine sand increases. While the buried depth is greater than the critical depth, the buried depth has almost no influence on the critical hydraulic gradient; meanwhile, the foundation has a strong ability to resist piping; its development of piping is similar to two-stratum dike foundation.

Key words: piping, critical hydraulic gradient, sand production, erosion