Abstract:Based on Newmark step-by-step implicit integration method,an improved method is put forward to improve calculation efficiency,and some questions are pointed out to which attention should be paid when initial static stress field is dealt with in dynamic nonlinear analysis. The implicit integration and explicit integration methods are applied,respectively,to calculate the dynamic response of a tunnel due to train vibration. It is shown that the improved method raise remarkably the calculation efficiency of implicit integration method and the required time of using implicit integration method is much less than that of using explicit method. It is suitable to select step-by-step implicit integration method to solve the questions of dynamic response for tunnel and some underground structures.