Dynamic Response Analysis on a Cross-Fault Tunnel Subjected to Action of Strong Earthquake After Fault Creep-slip
While fault creep-slip poses a risk to cross-fault tunnels in seismically active regions,intense ground shaking will impose more rigorous requirements on the safe functioning of the tunnel.Thus,the 100-year creep-slip dislocation of faults in the tunnel site area is calculated based on the Shantou Bay subsea tunnel,which crosses the active fault zone and is taken as the background and combining the actual engineering site characteristics and ground vibration parameters.A three-dimensional numerical calculation model of creep-slip-earthquake is established by taking into account the nonlinear plastic damage properties of the lining structure,and a study on the structural dynamic response of the tunnel to the initial damage caused by creep-slip of the fault is conducted.The results show that:(1)The tunnel has significant relative deformation near the fault fracture zone when it is only subjected to fault creep;the tensile and compressive impacts are more evident at the tunnel crown and invert,and the tunnel shows obvious shear state.(2)After the earthquake,the acceleration amplification phenomenon of the tunnel close to the fault zone becomes increasingly significant,with a maximum amplification factor of 3.0.(3)The horizontal deformation and arch waist strains of the tunnel following the ground shaking are significantly higher than the tunnel response under the single action of the superimposed ground slip.Maximum horizontal relative displacement is increased to 2.90 cm,and the equivalent plastic strain is multiplied up to five times.(4)The tunnel under the fault creep-lip damage is confined at the fault plane,and the ground shaking action amplifies the damage,resulting in cumulative damages to the tunnel arch foot and shoulder.(5)With greater initial creep-slip dislocations causing more severe damage magnitudes and larger PGA causing a wider range of damage,the effect of ground shaking following creep-slip dislocation enhances the tunnel damage response.The tensile damage lining volume of the tunnel under creep-slip-earthquake action can be enhanced by 224.8%when compared to the tunnel without creep-slip damage.The study findings can serve as a design guide for cross-fault tunnel seismic performance in the Chinese high seismicity areas.
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