The seepage deformation of the foundation pit excavation of power-house of a hydro-project is evaluated

based on probing into the method of evaluating the seepage deformation. The results indicate that along the axis of dam

the soil mass on slope of foundation pit is unsafe without impervious wall; when setting impervious wall

the hydraulic gradient on slope steps down to the value lower than 0.05; but the hydraulic gradient of the common boundary of base rock and gravelly medium-coarse sand is somewhat high; so seepage deformation may occur if water seeps out from fine sand soil and gravelly medium-coarse sand. On the whole

the probability of seepage deformation is small when setting impervious wall because the hydraulic gradient reduces to very small value.