Abstract: Gravelly soil has been widely used as impervious material in high earth-rock dam in recent years. Taking the 189m high Pubugou rockfill dam for example, the seepage stability experiment in the core wall material of Pubugou dam is described. The experiment results indicate that the content of fine material is the main factor which determined the seepage stability. Ways to distinguish fine-grained soil from coarse-grained soil, to calculate the optimal fine material content ,and to judge the seepage stability by fine material content are also compared. The test result addresses the assessment is valid that the gravelly soil can be the impervious body of a dam that which requires the content of grain size less than 5mm is more than 35% and grain size less than 1mm is more than 15%, while it is not regarded as an precondition that the grain size less than 0.005mm have to be more than 10%.

Key words: impervious material of gravelly soil, grain size critical content of coarse-to-fine particle, optimal fine material content, seepage stability impervious material of gravelly soil, grain size critical content of coarse-to-fine particle, optimal fine material content, seepage stability