Abstract: 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.

Key words: saturated soft soil foundation, high-speed train, 2.5D FEM, excess pore pressure, critical velocity