Seismic Analysis Of Mountain Tunnel By Finite/infinite Element Method

With the rapid development of high-speed railway,More and more mountain tunnels have been built.After the Wenchuan earthquake,the site investigation of earthquake damage showed that many mountain tunnels appeared serious damage,which has attracted the attention from the researchers and engineers.Studying characteristic of mountain tunnel subjected to seismic waves is meaningful for guiding the mountain tunnels design.In this thesis,a procedure of studying soil-stucture interation problem under seismic wave excitation is developed firstly,which combines the 2D finite/infinite element method proposed by Yang et al.(1996)and the procedure of equivalent seismic force proposed by Zhao and Valliappan(1993).Secondly,this procedure is used to study the wave propagation problems of the half-space and a half-space with a cavity excited by vertically incident seismic wave,the results show good agreement with the results of previous reseachers’ study,therefore,the reliability of the procedure is vertified.Finally,this procedure is adopted to analyze the seismic responses of single and twin mountain tunnels.A further parametric study of mountain and tunnel’s geometry and material parameters is performed.The major conclusions of the results has obtained:(1)The structure’s response due to SV waves is larger than the one due to P waves.With the excitation of the incident SV waves,the stress concentration of the single or twin mountain tunnel takes place: the peaks of the maximum and minimum principal stresses occur at the part between sidewall and the top of tunnel and the part between sidewall and the bottom of tunnel.For the twin tunnel case,the peak distribution of the principal stress on the adjacent side of the two tunnels is closer to the central line;the stress concentration occurs on the lining of single and twin mountain tunnels at sidewall,the top and bottom of tunnel due to the incident P waves.The interaction of adjacent side of twin tunnels is significant.(2)The amplitude of principal stresses the inner surface of the mountain tunnel linging is much larger than that of the outer surface,and the displacement and acceleration response of the inner and outer surfaces are consistent.(3)Due to the high stiffiness of the mountain-tunnel structure,and motion of the whole system is close to rigid body motion.The changes of material and geometric parameters of tunnel or mountain scarcely have little effect on the displacement response of the tunnel.The acceleration of tunnel linging of the upper part of tunnel is larger than the bottom part.(4)The stiffness and thickness of the lining only affect the magnitude of the principal stresses,and the principal stress distribution of the lining is unchanged.Within a certain range,the amplitude of the principal stress will reduce when the lining become thicker,but the effect is limited.It is suggested to determine the optimum lining thickness by numerical simulation for specific engineering projects.(5)When the tunnel passes through the weaker rock layer,the principal stress of the lining will greatly increase,which is harmful to the tunnel’s safety.It is recommended that the mountain tunnel should avoid crossing the weak rock layer.