The elastoplastic seismic response analysis of earth dam on deep sandy alluviums is an unresolved issue in the seismic study of earth dam due to the complexity of modelling the stress-strain characteristics of sandy soils and the instability of numerical computation. Elastoplastic seismic response analysis of an earth dam on deep sandy alluviums during M6.7 earthquake is carried out by using the u-p fully coupled finite element method for the saturated porous media and the multi-mechanism elastoplastic constitutive model for sandy soils. The dynamic behaviors of dam and foundation and the variations of the excess pore water pressure in generation

diffusion and dissipation are investigated. The results show that there are some differences between the calculated and measured values in accelerations and permanent deformations; but the calculated ones basically reflect their actual distributions; and then the certain accuracy of the constitutive model and numerical method is validated. Based on the numerical analysis results

it can be concluded that the reinforcement measure for the dam and its underlying foundation is not necessary

because the excess pore water pressures in these zones and the permanent deformation of the dam are small. However

an anti-liquefaction reinforcement measure should be taken since the excess pore water pressure is great and the liquefaction may occur in the shallow layer of sandy alluviums near the dam toe.