Abstract: A three-dimensional study is presented,where the steady state response of a track system and layered half-space soil medium subjected to the load induced by the passage of a moving train is investigated by the substructure method.Practically,due to the ground water table being of several meters beneath the ground surface,the soil profile can be divided into two layers: the upper layer modeled by elastic medium and the lower layer by fully saturated poroelastic medium governed by the Biot’s theory.In the meanwhile,the rails are regarded as an infinitely long Euler beam,and the sleepers are represented by a continuous mass.The effect of the ballast is accounted for by introducing the Cosserat model for granular medium,and the train is described by a series of moving axle point loads,depending on the geometry of the train.The influence of the thickness,mass and rigidity of the elastic layer and mass of the ballast on the displacement respons of rails is carefully investigated.Numerical results show that the influence of these parameters is significant under high train velocity,while insignificant under low velocity.