Abstract: At present the prototype monitoring is commonly used to know the seepage in performance period in earth-rock dam. Much research to stable seepage and there is no report about in-situ drilling tests of seepage during the first impoundment. In Pubugou hydropower station，the core-wall is such thin and not decorated with any monitoring instruments at early time above the elevation of 788.00 m. Weak areas of anti-permeability are revealed probably by the earlier monitoring, in-situ drilling tests of seepage is carried out in the core-wall during the first impoundment at 0+131and 0+434 section in August 2010. The results of the test analysis shows that, weak penetration area exists at some elevation of section 0+131and section 0+434 in the core-wall of Pubugou hydropower station. It also shows that under the necessary condition, in situ drilling tests in the core-wall during the first impoundment is practical and meaningful. The anti-permeability of fissured soil under the protection of reversed filter is suggested to be evaluated, the seepage monitoring in core-wall should be strengthened to inspect the safety of the core-wall. The experiment researches provide a reference for other gravel soil core wall of the dam design, construction, and the safety of the operation period.

Key words: earth rock dam, permeability test, core wall, fisrt impoundment