| With the development of China’s transportation construction,a large number of tunnel projects will inevitably be built in the western region of China where the earthquake is strong,while shallow-buried tunnel openings in high-intensity earthquake areas are one of the most severely damaged areas.The simplified seismic calculation method of tunnel structure can quickly and accurately obtain the internal force and deformation of the structure under the action of earthquake,but there are few researches on the seismic calculation method of tunnel structure at the entrance.This thesis is funded by the National Natural Science Foundation of China "Research on Multi-segment Partitioned Damping Technology for Structures Across Active Fault Zones under Strong Earthquakes"(No.51778540),relying on an oil pipeline tunnel in Central Asia,the applicability of the simplified seismic calculation method for the portal section of tunnel is studied,and an improved method for the seismic calculation of the structure at the portal section is proposed.The main research contents of the thesis are as follows:(1)The calculation errors of the four seismic calculation methods are compared and analyzed,and the applicability of the seismic calculation methods in the tunnel entrance section is studied.The results show that the integral response displacement method has the smallest calculation error under different burial depths,and the maximum calculation error is only 17%,which shows that they all have high calculation accuracy;however,in the seismic calculation of tunnel portal structures,the calculation results of the four methods have large errors,and the calculation errors are more than 60% when the burial depth is 6m,which shows that the commonly used simplified seismic calculation of tunnels is difficult to apply to the seismic calculation of tunnel portal structures.(2)Aiming at the error source of the tunnel seismic calculation method applied in the tunnel portal section,by introducing the structural displacement amplification factor,an improved integral response displacement method suitable for the tunnel seismic calculation of the tunnel portal section is proposed.The influence of different tunnel entrance elevation slope angle,slope height,peak acceleration and weak surrounding rock cover on the structural displacement amplification factor is studied.The law that the structural displacement amplification factor will increase with the increase of slope height,slope angle,seismic wave peak acceleration,and the difference between the overburden and the underlying rock mass is obtained.A fitting calculation formula for the influencing factors of the structural displacement amplification factor is established(3)Aiming at the difficulty of seismic calculation of tunnel structure in the high-intensity earthquake area under complex environmental conditions,a large-scale shaking table test of the tunnel entrance structure is carried out in this thesis.The response law of acceleration,strain and bending moment of the tunnel structure under different ground motions is studied.The research shows that the peak acceleration of the tunnel structure decreases with the increase of the distance from the tunnel;the response law of the strain and internal force of the lining is similar,and the peak value of the internal force and strain of the lining increases with the distance from the tunnel and the peak intensity of ground motion.The theoretical calculation results,test results and time history analysis method results before and after the improvement are compared and analyzed.The calculation results of the improved integral response displacement method in the opening section can not only completely envelop the time history analysis results and the model test results,but also the calculation errors are not more than 20%,it shows that the improved integral response displacement method can be applied to the seismic calculation and analysis of tunnel portal structures. |
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