Whether the seepage failure will occur in gravelly soil under high water head to a great extent depends on the protection effect of the filter on the gravelly soil. Based on many combination seepage failure tests of the gravelly soil and the filter using self rebuilded vertical permeameter,the influence of the gravel content and dry density of gravelly soil, the grading, dry density and thickness of filter on the seepage failure resistance was studied.Occurring mechanism of the initial critical hydraulic gradient and the formation process of self filter layer were analyzed.The results showed that the initial critical hydraulic gradient increases with the increase of the dry density of e gravelly soil and filter.It decreases with the increase of the gravel content of gravelly soil and the control particle size D15 of filter.In addition,the initial critical hydraulic gradient increases with the increase of the thickness of the filter.
