Abstract: A state of the art is briefly reviewed on rutting in flexible pavement foundations under cyclic loading.Based on the dynamic soil- pore water coupled system theory,this paper focuses on the numerical modelling of rutting in flexi ble pavement foundations under plane strain condition.A new simple viscoelastic dynamic model for predicting the cyclic response of soils is developed to predi ct the nonlinear response of pavement materials under cyclic loading.The propos ed model takes into account the shear modulus,the damping ratio,pore water pre ssure and permanent deformations of pavement foundation materials.An illustrati ve example is given for the prediction of rut depth development in a flexible pa vement.