Visco-elastic Imperfect Bonding Effect On Dynamic Response Of Tunnels

Underground tunnels are a kind of engineering buildings buried under soil.Compared with the upground structure,the tunnel structure has significant difference in the environment of occurrence and mechanics.The surroundings of the tunnel are closely contacted with the surrounding rock,the load on the tunnel structure mainly result from the surrounding rock pressure that caused by the deformation or loosening of the surrounding soil caused by the excavation of the cave,and the deformation of tunnel structure under the action of load is restricted by the surrounding rock.There are many microstructures that destruct the contact surface between the tunnel and the surrounding rock such as fine cracks and impurities.Therefore,based on the theory of visco-elastic interface,the mechanical behavior between the tunnel and the surrounding rock is demonstrated reasonably,the dynamic response of the tunnel structure under the external load is studied.The main contents are as follows:By combining the wave function expanded method and the conformal transformation method,the analytic solution of the displacement and stress around a semicircle and straight wall tunnel with elastic interface under anti-plane shear wave is given.The elastic interface around the tunnel is modeled by the spring model.Through some numerical analysis,the influence of the elastic interface on the dynamic response of the tunnel under different frequency of elastic waves is obtained.When the frequency of incident wave is low,the vault and the bottom of tunnel have stress concentration obviously.In the case of the intermediate wave frequency,the material with small stiffness coefficient should be chosen on the side of the elastic wave incident,and on the another side should chose the material with large stiffness coefficient.When the frequency of incident wave is high,the stiffness coefficient of the lining on the side of the elastic wave incident should be improved.The dynamic response of the tunnel under dynamic load is studied by establishing a visco-elastic model with time dependence and using the complex function method,the conformal transformation method and the wave function expanded method.Through some numerical examples,the influence of stiffness coefficient and viscous coefficient on the dynamic response of tunnel is analyzed in detail.When the frequency of incident wave is low,the dynamic stress decreases with the increase of the viscosity coefficient.With the increase of stiffness coefficient,the influence of viscosity coefficient on the dynamic response of the tunnel will decrease.When the frequency of incident wave is high,the maximum stress occurs at the vault and the bottom of the tunnel,and the influence of the visco-elastic interface on the dynamic response of the tunnel is significantly lower than what when the frequency of incident wave is low.The dynamic stress distribution around the semicircle and straight wall tunnel in saturated porous media is accurately predicted by combining Biot's theory and visco-elastic interface model.The viscoelasticity of the interface is considered by introducing the stiffness coefficient and the viscous coefficient.Some numerical solutions are given to analyze the effect of the interface characteristics on the dynamic response of the tunnel under external load.When the frequency of incident wave is low,the dynamic stress at the vault and the bottom of the tunnel increases with the decrease of the interfacial viscosity coefficient,and the influence of the interfacial viscosity coefficient on the tunnel will increase with the decrease of the stiffness of the saturated porous media.When the frequency of incident wave is high,the dynamic stress around the tunnel decreases with the increase of the interfacial stiffness coefficient.The influence of visco-elastic interface on the dynamic response of the tunnel decreases with the increase of wave frequency.