Research On Some Problems In Dynamic Analysis Of Underground Structure

As the rapid development of tunnels and underground structures, the dynamic response analysis of such structures is of great economic and social significance. In this thesis, the responses of tunnels are numerically analyzed under dynamic loading by finite element method. The contents in this thesis are concluded as follows:1. The seismic response analysis and back analysis of layering level soil is performed using wave theory. Effects of frozen soil layer and radiant damp of foundation soil on site earthquake responses are studied in detail. The seismic wave that is prerequisite at the seismic responses calculation of structure is obtained by using back analysis.2. The computing precision of three type conditions such as viscous-spring boundary, viscous boundary and fixed boundary is compared. Based on various boundary conditions, the seismic response studies of a tunnel are executed by using vibration-method and wave-method respectively. The influence of infinite foundation soil on the earthquake responses of the tunnel is researched and the weakness parts in liner are determined.3. Based on Newmark's step-by-step implicit integration method, an improved method for raising computing efficiency is put forward. The implicit integration method and improved method were applied respectively to analyze the dynamic response of a tunnel due to train vibration. Results indicated that the improve method economizes computer memory and enhances remarkably the calculation efficiency and it will be adopted in many computational programs.4. Based on Newmark's step-by-step implicit integration method, the response analyses of a tunnel are performed by using viscous-spring artificial boundary under various earthquake accelerations and multiform conditions of surround rock. The seismic responses of the tunnel are calculated by changing parameters of surround rock within the tunnel some ranges. Two kinds of shock absorption measures, which are setting shock layer and reinforcing surround rock are studied and shock absorption effects, applicable to cases and shock mechanism are analyze. The viewpoint of adopting the method reinforcingsurround rock for shock absorption purpose is proposed which is able to exert carrying capacity of surround rock, and it will be beneficial for the anti-seismic design of tunnel.5. Based on Newmark's step-by-step implicit integration method, 3-D seismic responses of tunnels are performed by using viscous-spring artificial boundary. The orderliness of stresses and displacements in the liner along the direction of the tunnel axial are analyzed under various type tunnel liner and multiform properties of surround rock. The effects of shock absorption measure reinforcing surround rock are studied. The relation between the strengthening length of the tunnel anti-seismic and the properties of surround rock of tunnel entrance and the shape of tunnel liner is analyzed. The axis direction stress in tunnel entrance is not slighting under earthquake loading. The results provide references for the anti-seismic tunnel design.6. The problem of determining dynamic loading history by using the back analysis is discussed. On the basis of the solution for dynamic equilibrium equations utilizing the Newmark method, an algorism for evaluating dynamic loading is presented. The creditable loading coefficients are estimated by using the method of least squares. Then the finite element method for evaluating dynamic loading history was carried out by using the measured structure responses under the same loading. An example is given to verify the effectiveness of the proposed technique. It is a new method for computing vibration loading and it will help to solve some vibration problems.