Based on Biot’s theory and considering the property of moving loads

the boundary integral equations in the frequency domain-wave number for semi-infinite saturated soil is obtained by using the integral transform methods. The Cauchy type singularity of the 2.5D boundary integral equation is discussed and the effectiveness of passive vibration isolation using the open trench on the saturated soil is analyzed. Comparing the result with an existing one shows a good agreement. Numerical results show that

the present 2.5D boundary element method (BEM) is not only adaptable to solve the dynamic responses of moving loads with complicated boundary conditions

but also the computation time can be decreased greatly. For moving loads with high velocity

a considerable oscillation reduction of the pore pressure and the vertical displacement can be achieved by using open trench. The open trench barrier has no effect on the horizontal displacement for moving loads with lower velocity

even has the amplificatory effect on the vibration. Moreover

with the increasing of the distance between the vibration source and the open trench

the isolation effect of the surface wave propagation may be improved.