Study On Seismic Dynamic Response And Countermeasures Of Tunnels Through Active Fracture Zones

A large number of post-earthquake investigations show that the active fault zones are the most severely damaged sections of the tunnels under earthquake,which seriously affects the safe operation and service life of the tunnel.Therefore,relying on the Bailongjiang Water Diversion Project,this paper takes the Liupanshan Tunnel passing through the Liupanshan Active Fault as the research object.Based on the analysis to the regional geological backgrounds and the fault activities,the threedimensional seismic dynamic responses of the tunnel section passing through the active fault（TSPAF）are studied by many methods including numerical modeling.The spatiotemporal characteristics of the 3-D seismic dynamic response of the TSPAF before and after the damping measures are analyzed.According to these,the shock absorption mechanism of the damping measures is explained,and their evaluation standards is put forward.The main results are as follows:（1）The time-history variation law of the initial acceleration of the 3-D seismic waves and the size of the peak value have a controlling effect on the acceleration,displacement,stress time-history and peak value of the tunnel lining structure.The characteristics of incident waves play a key role in the analysis of engineering seismic dynamic response.In addition,there is a lag in the arrival time of the peak acceleration of the lining,and the maximum,minimum principal stress and maximum shear stress of the lining have obvious time-history accumulation and amplification effects.（2）The dynamic response of the tunnel rock mass and lining structure in the TSPAF has a significant amplification effect.The acceleration,stress and deformation of the surrounding rock and lining in the TSPAF are significantly greater than those in hanging wall and footwall blocks of a fault,and there is a significant mutation at the interface between the two.（3）The dynamic response of the surrounding rock and lining in the tunnel section of the TSPAF has significant anisotropy,in which the radial and axial acceleration peaks of the tunnel are significantly amplified at the tunnel lining side walls,while the vertical acceleration peaks at the tunnel vault.The magnification of the inverted arch position is more significant.Tensile stress distribution appears in the lining structure of the fault fracture zone,among which the tensile stress and shear stress of the inverted arch and the arch foot are relatively concentrated,indicating that the inverted arch and the arch foot are the weak parts of the lining for earthquake resistance.（4）The shock absorption layer and the aseismatic joint can improve the stress state of the tunnel lining in the section of the fracture zone by absorbing the seismic energy,thereby improving the seismic level of the fracture zone of the tunnel.The specific shock absorption effect is mainly reflected in that the setting of shock absorption layers and the aseismatic joint can reduce the peak stress of the tunnel lining structure,the amplitude of oscillation of the lining stress and deformation during the earthquake period,and the peak acceleration of the lining.