Study On Dynamic Response And Seismic Isolation Mechanism Of Longitudinal Joints In Tunnel

The western area of China is located on the Qinghai-Tibet Plateau.It has complex geological structures,strong crustal movements,and frequent seismic activities.With the implement of the Great Western Development,a large number of traffic and hydraulic tunnels have been or will soon be completed,and all of them undoubtedly take risks of strong seismic hazards.In order to protect the tunnels,it is significant to conduct the research related to the seismic isolation techniques and mechanism for the tunnel engineering.Relying on the Galongla tunnel engineering,this paper was focused on the seismic isolation joint and conducted the research on their dynamic response and seismic isolation mechanism using multiple methods such as theoretical analyses,in-house model tests and finite element numerical simulations.The main contents are as follows:(1)Considering the longitudinal propagation path of seismic waves,based on the elastic stress wave theory,a theoretical model of seismic isolation joint was established.Then,based on the established model,a discriminant which is used to evaluate the seismic isolation effect was given,then the seismic isolation effect was evaluated by comparing the amplitude of seismic wave before and after crossing the isolation joint.At last,the accuracy and applicability of the theoretical model and the discriminant were checked and confirmed.(2)The dynamic tests of asphalt and rubber were conducted,and their dynamic response were studied.The test results showed that the dynamic modulus of asphalt grows with the increase of loading frequency,however,the growth rate tends to become lower when the modulus reaches a particular value.On the other hand,the dynamic modulus of rubber basically remains steady in the domain of seismic frequency.(3)By means of biaxial dynamic loading machine and optical camera,the cyclic loading and strain monitoring tests of concrete-seismic isolation joint model were made within the seismic frequency and the seismic isolation mechanism of tunnel joints were studied,in which different elastic modulus and thickness of rubber were considered and 18 cases were set.The test results suggested that the seismic isolation effect tends to be better when the elastic modulus is lower or the thickness is greater.(4)Relying on the Galongla tunnel engineering,based on the finite element numerical simulation technique,the seismic isolation mechanism of tunnel joints were studied,in which multiple factors such as elastic modulus,thickness,spacing,amount and position were considered and 32 cases were set.The results suggested that the seismic isolation effect tends to become better when the elastic modulus is lower,the thickness is greater,spacing is smaller,the amount is greater,the position is farther from the tunnel portal.The weights of the five influencing factors were calculated,that was 36:14:48:25.(5)Relying on the Galongla tunnel engineering,combined with the portal model and case settings,the applicability of the seismic isolation joint was discussed.The results suggested that asphalt could meet the requirements of 7-Degree seismic fortification,and rubber could even meet the requirements of 8-Degree seismic fortification.In addition,the optimum solution of isolation joints is as follows:styrene-butadiene rubber,the thickness of 20 cm,the spacing of 10 m,the amount of 3 layers and 5 m far from the portal.