The Seismic Response Of Mountain Tunnels Passing Through Weathered Ditch

The construction cost of mountain tunnel is very exorbitant, and the maintenanceand reconstruction cost are even higher if tunnel failure happens. Tunnels may sufferfrom cracks or even collapse when subjected to seismic loads. To make matters worse,mountainous regions are characterized by complex geological conditions, and thatcontributes to the difficulties in investigating the seismic response of mountain tunnelsconsidering many influencing factors. In this thesis, the analytical and numericalmethods are combined to investigate the seismic response of mountain tunnels passingthrough weathered ditch. A series of prediction methods are put forward andcorrespondent numerical simulations are performed to verify the theoretical approachesmentioned above.To begin with, two ways are adopted to simplify the forced vibration of free fieldunder seismic effect. In the Single-Degree-Of-Freedom-Method (SDOFM), thehomogeneous freefield is simplified as a shear element with only one degree of freedom.In the Infinite-Degree-Of-Freedom-Method (IDOFM), the homogeneous freefield isdivided into numerous soil columns. These columns are regarded as cantilever beamswhich only undergo shear deformation. Then the vibration equations are established toobtain the analytical solutions of both methods. And the correspondent simulationmodels are established to verify the numerical methods. The results show that SDOFM issimple but only applied to hard rocks, while the IDOFM can be applied to a wider rangeof homogeneous fields, and with considerable accuracy.Secondly, to consider the interactions between the unweathered rock (UR) andweathered ditch (WD), a sandwich model of UR-WD-UR structure is eatablished tofurther the mathematical modeling and solution of the geological condition. Based on theIDOFM, the interaction between UR and WD is simplified as a spring system. Thecoupling equation system is established and solved using inverse method. Then thenumerical verification is performed, showing the sandwich model can be used to predictthe displacement response of the field, and with fair accuracy.Thirdly, the seismic response of field is regarded as excitation for the tunnel, and the tunnel is simplified as a finite beam with both ends fixed. The governing equation of thetunnel is established based on the Primary Beam Theory and then solved. The numericalverification is finally conducted, showing the analytical method can factually reflect themechanism of the seismic response of tunnels, and with fair accuracy.Finally, a three-dimensional finite difference model is established to make up for thedeficiency of theoretical model. The processes of excavation, support and stress releaseare carefully simulated to form the initial stress field. Then apply seismic exitation andanalyze the stress and displacement response of tunnel cross sections. A wide range ofparametric studies are carried out to investigate the influences of tunnel structure and sitecondition to the seismic response of the tunnel.