Abstract: The saturated soil exits widely on the earth. The soil should be considered as two phase medium of solid and fluid. The equivalent viscous-elastic artificial boundary element is studied regarding the effects of energy radiations of solid-fluid medium based on the u-p type of Biot equation of saturated soil. The wave input is realized by the equivalent load of earthquake on the node of artificial boundary. Its calculation precision is verified by comparison the examples. A nonlinear finite dynamic model of saturated soil-subway station is proposed for analyzing the wave propagation of soil in two phase medium and comparing with the seismic response in saturated soil and single phase soil under earthquake. The numerical results are compared with the results obtained from shaking table test. The results are shown that it is more reasonable to use the characteristics of multi-pore medium to analyze foundation soil under earthquake motion than to use the single phased medium. The seismic response of saturated soil and underground structural interaction system is studied through analyzing the acceleration, displacements and internal forces of the key elements in the station.

Key words: underground structure, equivalent element of viscous-elastic artificial boundary, subway station structure, saturated soil-structural dynamic interaction