Damping Mechanism Study Of Shallow Tunnel With Shock Absorption Layer Based On Wave Motion Theory In Strong Earthquake Region

The shallow tunnels are prone to seismic damage during strong earthquake,and more and more tunnels will be built in high intensity earthquake region with the rapid development of China's rail transit construction,therefor it's a great importance to study the dynamic reponse and shock absorption measures of the shallow tunnel in high intensity seismic region.In this dissertation,two kinds of mechanical models of shallow buried tunnel subjected to plane P,SV or Rayleigh waves are established using Fourier-Bessel function expansion method,such as "Surrounding rock-Shock absorption layer-Liner" and "Surrounding rock-Initial Liner-Shock absorption layer-Secondary liner".The factors affecting the dynamic response of the tunnel is discussed,such as the tunnel depth,the angle of incidence wave and the incidence frequency,and the influence of the ealstic modulus and the thciness on the damping effect with shock absorption layer is also analyzed.Finally,based on the shallow tunnel in Jakarta-Bandung High-speed Railway project,based on the theoretical analysis and finite element analysis,and compared with the shaking table model test,the dynamic response of the tunnel is deeply studied,based on the main work and some conclusions are as follows:(1)The results of theoretical analysis show that the dynamic response of the shallow tunnel subjected to plane P,SV or Rayleigh waves make a big difference,the maximum dynamic stress concentration factor of the tunnel liner reaches to 17.7 caused by the low frequency vertical incident plane P waves,appears in the tunnel hance,and the associated value changes to 33.1 for the low frequency vertical incident plane SV waves,appears in the tunnel spandrels and foots,and the maximum dynamic stress concentration factor of the tunnel liner approaches to 8.4,appears at the left foot of the tunnel.(2)The ratio of the tunnel depth h and the incident wave length ? has a significant influence on the tunnel dynamic response,the tunnel dynamic stress is small when the tunnel depth h is even times of the 0.25 times the wave length,however the tunnel dynamic stress changes large when the tunnel depth is odd times of the 0.25 times the wave length,and for the earthquake wave oblique incidence,because on the surface of the earth complex waveform conversion,the law is complex.The associated value is efficently reduced as the tunnel depth decreases when the tunnel is subjected to Rayleigh waves,and the ground surface has great influence on the tunnel dynamic response when the buried depth is less than 0.5 times the length of seismic shear wave.(3)The incidence wave angle and incidence frequency have a significant impact on the tunnel dynamic response.The low frequency incident waves always have a greate influence on the tunnel dynamic response,and when the incident angle of seismic wave is close to the critical angle,the dynamic response of the tunnel is larger,and the dynamic stress concentration factor is very small when the incident angle is close to the horizontal incidence.(4)The maximum dynamic stress of the tunnel liners decreases when the shock absorption layer is set between the liner and the surrounding rock,and the associated value of the secondary liner is also reduced with the shock absorption layer set between the initial liner and the secondary liner,while the corresponding value of the initial liner increases greatly,and the shock absorption layer between the liners has a better damping effect.However the dynamic stress becomes lager when the elastic modulus of shcok absorption layer is too low or its thickness is too bigger,then the ratio between the thickness of the shock absolption layer and the tunnel diameter is proposed to 1/40?1/20,and the elastic modulus ratio between the shock absorption layer and the surrounding rock is suggested to 1/50?1/100.(5)Based on the time-domain wave method with viscous-spring absorption boundary condition,a input method for the plane seismic SV waves of oblique incidence is proposed.Based on the Jakarta-Bandung High-speed Railway project,the finite element dynamic time history analysis of shallow buried tunnel subjected to the oblique incidence wave is carried out,and some numerical results are given:1)Seismic wave displacement is the main factor to control the internal force of the tunnel compared with the wave acceleration or velocity.2)The incident angle of seismic wave affects the dynamic stress and deformation of the tunnel significantly,and when the wave incidence angle increases,the relative displacement of tunnel becomes lager,and the liner shear force and axial force increases obviously,while the bending moment dose not change significantly,finally the maximum principal stress of the tunnel liner increases significantly as tunnel dynamic rock pressure increasing.(6)The finite element dynamic time history analysis of the shallow tunnel subjected to seismic waves with shock absorption layer is carried out,such as the "Surrounding rock-Shock absorption layer-Liner" tunnel and "Surrounding rock-Initial Liner-Shock absorption layer-Secondary liner" tunnel.The numerical reslts indicate that the shear foce and the axial force of the secondary liner are reduced by about 50%with shcok absorption layer being set between the surrounding rock and the liner or between the initial liner and the secondary liner,while the bending moment increases to some extent,and the maximum principal stress is absolutely reduced in general.It is noteworthy that the shock absorption layer between the liners has a better damping effect,while the dynamic stress of the initial liner increases obviously.(7)The dynamic stress response of the tunnel subjected to shear waves is in good agreement with each other using the finite element analysis and theoretical analysis,when the shock absorption layer is set between the surrounding rock and liner,the maximum dynamic stress of the liner is reduced about 16%,while the associated value can significantly decrease around 40%when the shock absorption layer set between the initial liner and secondary liner.The tunnel shaking table model test results show that the number of tunnel liner cracks decreases when the damping layer being arranged betwwen the surrounding rock and lining,and the secondary liner remains intact with the shock absorption layer set between the initial liner and secondary liner,however the initial liner was badly damaged.(8)Based on numerical simulation of vertical vibration load induced by high speed train,the dynamic response of the shallow buried tunnel with shcok absorption layer has been analyzed using elastoplastic finite element method.The vertical displacement,vertical acceleration and the maximum principal stress under of the tunnel vertical vibration load are discussed,and the results show that the vertical vibration load has little effect on the vertical diaplacement and the dynamic stress of the tunnel with shcok absorption layer,however the peak acceleration of the secondary liner increase obviously.