Abstract：The soil layers with liquefaction characteristics can be often found in the foundation of earth-rock dam in plain area. The soil liquefaction under seismic loading and its influence on the stability of the dam are important issues. The Erwangzhuang reservoir dam，a typical earth-rock dam in plain area，is chosen as an example to study the problem. Based on the indoor and in-situ tests，the liquefaction possibility of the soil layers，the dynamic properties of soil and the change of seepage field in the soil under earthquake are all concerned. The in-situ test results show that under seismic loading with magnitude 7，some in-situ soil layers could be liquefied. The results of indoor model tests show that the seepage field in the soil is changed under vibration；but the change of seepage field is not obvious. Utilizing the soil parameters obtained by indoor tests，the dynamic numerical analysis is performed with/without considering seepage. The numerical results show that the depth of liquefied zone agrees with the results of tests. The size of liquefaction region in the foundation is affected by the distribution of soil layers remarkably；yet the seepage influence is not obvious. When considering seepage，the factor of safety of upstream increases and the factor of safety of downstream will decrease. The influence of the seepage on the horizontal displacement can also be found at the same time.
