The Study Of Seismic Response Of Shield Tunnel Crossing Interface Of Soft And Hard Strata

With the rapid development of urban subway transportation, shield tunnel method has gradually become the first choice of urban tunnel construction for its safeness in excavation and quickness in construction. And as time goes by, shield tunnel is becoming rich in structure type and the strata the tunnel crossing is becoming more and more complex. In the past, people thought that the underground structure was "free of earthquake structure". But in recent decades, a large number of underground structure have been destroyed in earthquakes, which has a great influence on the society and economy. So, it is necessary to study the seismic response characteristics and seismic performance of underground structure. To study the seismic response characteristics of the shield tunnel crossing the soft and hard strata, this paper has conducted numerical simulation analysis and shaking table test based on the project of Xiamen metro line two project.Firstly, the mixed scale 3D finite model of the tunnel and surrounding ground is built in Abaqus software, and this model was used to simulate the seismic response of the shield tunnel crossing the interface of soft and hard strata taking different seismic waves, the variance of seismic wave input angle, the change of interface angle into consideration. Result shows that the soft and hard ground share the same acceleration response rules, but difference in value, the maximum principal stress of tunnel lining increase greatly around the interface, and this trend is most obviously when the propagating direction of shear seismic wave is perpendicular to the axis of tunnel. Change of the interface angle will also affect the value of the maximum principal stress, but this effect is not significant. The angle between the seismic propagation direction and the tunnel axis determines the inner force of the bolt, the value of the inner force and type inner force will change when the seismic wave is input from a different angle. Then, the results of the numerical simulation are verified by shaking table test. Experimental result shows that due to the nature of the formation of different strata conditions the soft strata’s acceleration amplification trend is much more obvious, but the acceleration response of the two kind of strata still has the same characteristics at the same height, principal stress concentration phenomenon occurs at the interface of soft and hard stratum as the simulation results shows.