Abstract: For the engineering background of a typical subway tunnel with initial defects caused by the construction of the new down-through tunnels in Beijing, the aseismatic performance of the existed tunnel is studied so as to reveal the mechanism of seismic dynamic response by using finite difference method. Numerical model will firstly be established. Then its boundary conditions and initial conditions are considered, including the choice of related parameters and seismic wave at the same time. The numerical simulation results show that the tunnel is deforming in its entirety since such physical variables as displacement and stress in its all key weak points have the same dynamic tendency under the influence of approaching construction of tunnels, and the variables including displacement and stress are much larger than those without any influence. For examples, after down-through construction, much influences of aseismatic performance are mainly taking place at both the side wall and the upper arch; and the shearing damage are mainly doing in surrounding soil mass. Due to widely shearing damage after down-through construction, it is suggested that grouting reinforcing should be applied so as to make them much stiffness as a whole and to have good aseismatic performance.

Key words: finite difference method, existed tunnel, initial defects, seismic dynamic response