通过粉煤灰坝工程实例分析，探讨其灰体渗漏的原因，并分析渗漏的机理。根据反滤层土拱破坏效应和灰体-反滤体颗粒级配效应，提出渗流破坏的有效粒径比Ra=8和Ra=12作为阀值，来划分为渗流冲刷的稳定、敏感和破坏区域。认为灰体、反滤层和渗流坡降是一个相互作用的有机整体，并在此基础上确定了压密状态下反滤层破坏的临界渗流坡降Jcr的计算模式。

The seepage erosion of fly ash dam is rarely documented. A case study is presented in this paper. What causes the erosion occurred is the failure of ash-filter system under variable confining pressures. The effective grain-size ratio (Ra) between the coal soil as filter and the flyash as an erosion medium is 10.15, which shows susceptible to bringing on seepage erosion under a given seepage force while the susceptible limit Ra are Ra > 8 and Ra < 12. Base on the understanding of the reciprocity among fly ash, particle filter and seepage gradient, the critical seepage force can be ascertained as follow. In this formula, the critical gradient can be easily calculates after some parameters have been known such as pore ratio(e), effective diameter (ds85), mechanical index ψ & C, and depth of fly ash.