Seismic liquefaction of deep-sand lens in a dam foundation is evaluated by two processes. Firstly

specification methods are used to make preliminary and again judgment. Secondly

Seed and Dobry methods are used with dynamic triaxial test results to make more evaluation. Various estimation methods are analyzed synthetically. Based on the analysis results and considering the practical engineering conditions

a conclusion that a special treatment is needn’t made for deep-sand lens in dam foundations

is drawn.