Study On Nonlinear Seismic Response Of Rock Tunnels

The investigation of the seismic damage to the rock tunnels by some recent earthquake, such as Kobe(1995), Chi-Chi(1999) and Wenchuan(2008), indicates that the rock deformation and the fault slip are the main influencing factors affecting the seismic damage in tunnel. Accordingly, the dynamic response analysis of rock tunnels under seismic waves is of great theoretical and engineering significance. As a nonlinear near-field wave motion problem, the dynamic response of rock tunnels is under the control of the properties of seismic waves. Apart from this, the topography,geomorphology and the geological conditions also have a great impact on this engineering problem, such as fault effect, spatially non-uniform effect, material nonlinearity effect and so on. Base on the nonlinear near-field wave motion theory, the study on the seismic response of rock tunnels is produced in this paper.The main efforts are summarized as follows.1. Within the theoretical framework of the nonlinear near-field wave motion theory, the mechanical constitutive model of rock mass and the input method of seismic waves are developed.(1) On the basis of the concept of effective stress and the strain equivalence hypothesis and combining with the nonlinear unified strength model as the yield function, a three-dimension elastic-plastic damage constitutive model of rocks is presented. Comparison between the present theoretical results and the material-test data is produced, which indicates that the presented constitutive model can describe the strength and deformation behaviors of rock well, also the strain softening behaviors of rock.(2) Coupling the explicit finite element method with the viscous-spring artificial boundary condition, the oblique input method of plane seismic waves in proposed, for homogeneous site and site with fault in three dimension. A simplified seismic wave input method are also established for vertical incidence of plane waves; Afterwards, contrast of the wave and vibration input methods for underground structures are conducted. Furthermore, a new vibration input method considering free-field motion on the artificial boundary is deduced.2. Based on the time-domain wave method coupling the finite element method, the dynamic analysis of rock runnels subjected to earthquake is conducted. The detailed efforts are given as follows:(1) With the three-dimension elastic-plastic damage constitutive model of rock, the dynamic response of tunnel under vertically incident earthquake is simulated. The impact of the vibration direction of seismic waves on the response of tunnel is studied.(2) The seismic response of long lined tunnels is studied subjected to seismic waves with different incident angles, by the oblique incident method of plane waves in three dimension. The relationship of the deformation of tunnel lining and the incident angles of seismic waves is investigated.(3) The seismic response of bias tunnel in jointed rock slope is analysised. A jointed model was adopted to modeled the jointed rock. The simulation results indicated the failure model of bias tunnel in jointed rock slope, as well as the influences of joints angle and incident angle of seismic waves.(4) Study of dynamic response of rock tunnels through fault fracture zone is developed under seismic waves, with the incident method of plane waves for site with fault in three dimension. Impact of incident angles of seismic waves, width and mechanical properties of fault on the seismic response of tunnels is analysed.