Based on the Biot theory of porous media

this paper proposes a coupled vehicle-track-saturated foundation model to study the dynamic responses of saturated soft soil foundation under high speed train via two-and-half dimensional finite element method (2.5D FEM). It is found that the ratio of train speed c and soil Darcy permeability ( ) determines the extent to which maximum excess pore pressures build up in saturated soft soil under the train load when the load speed is lower than the critical speed. For a saturated soil of a particular stiffness

if is less than or equal to 3×104

the soil can be viewed as highly permeable in relation to the load velocity and almost no excess pore pressure is developed

the saturated soil can be modeled using single-phase medium. There is a critical value of for the development of excess pore pressure

when is smaller than the critical value

the maximum excess pore pressure increases with increasing . Above the critical value of

the maximum excess pore pressure remain independent of . The amplitude and affect scope of effective stress are mainly controlled by train speed and soil permeability for saturated soft soil foundation. The response of displacement is mainly controlled by the train speed. Significant Mach effects have been induced in the saturated soil foundation by the moving train

when the train speed reaches or exceeds the critical velocity of the track-foundation system.