| With the strategy “The belt and Road” of our country,the central and western railway construction investment to further increase,safety problem of tunnel in loess seismic area is becoming more and more serious.Such as the constructed railway Bao Lan passenger line,Lan Yu railway,and is being build railway Cheng Lan railway,Yin Xi railway et al,all of them through the loess seismic belt.The location of tunnel through the mountain is mostly designed to satisfy the plane alignment and elevation settings,influence of tunnel elevation on seismic fortification of tunnel portal is not considered.At present,there are many achievements in the study of rock mountain tunnel in academic circles,many experts and scholars have paid enough attention to the seismic resistance of tunnel portal section,however,due to the lack of actual seismic data,the study of loess tunnel is relatively backward.However,as an important parameter that influences the dynamic response of the loess tunnel,the entrance elevation of the tunnel on slope is rarely concerned.Therefore,In this paper,the entrance elevation on slope is taken as a key parameter,aimed at the different entrance elevation tunnels' characteristics of seismic hazard,by means of shaking table model test and numerical simulation analysis,studied the qualitatively characteristics of dynamic response of slope-tunnel system.The main research contents and conclusions are as follows:(1)Based on the investigation of the seismic damage mechanism,seismic design method and anti vibration measures of the tunnel portal at home and abroad,this paper summarized the characteristics of the elevation amplification effect of the tunnel slope and the seismic wave amplification effect of the tunnel lining structure,the research ideas and contents of this thesis are put forward.(2)According to the background of the selected topic,the research content and the purpose,the experimental conditions,the large scale shaking table model test of the slope-tunnel system portal with the ratio of 1:70 is designed,the foot slope into the tunnel and the 1/2 slope height into the tunnel model test seismic hazard shows that: Slope-tunnel system's slope height,slope angle,incident seismic wave,rock and soil material,filling method and structure of the lining both are the same,only different the height of the entrance elevation,the forms of tunnel entrance destruction is different,the degrees of damage divided.To the loess tunnel seismic wave in X,the side slope of the entrance is more likely to suffer seismic damage than that of the tunnel structure.The main forms of earthquake damage are the cracking,collapse,instability and seismic subsidence,the seismic inertia force caused by seismic wave vibration effect is the main factor affecting the seismic damage.(3)In the two group model tests,the characteristics of seismic damage of tunnel crossing slope and tunnel without crossing slope show that,the tunnel crossing slope seismic damage is more serious than that of the side slope without tunnel under,tunnels' entrance elevation more bigger slope failure more earlier,and the more serious the damage near the portal.The lining structure of tunnel entrance has obvious amplification effect on seismic wave,the tunnels' entrance elevation more bigger,the amplification effect more remarkable,the superimposed wave field formed by seismic wave propagation effect determines the failure mode of slopetunnel systems.(4)Embedded monitoring element in representative characteristic parts of two sets of shaking table test model,through the comparative analysis of monitoring data,horizontal incident excitation along parallel to the tunnel axis,with the increase of excitation amplitude,the acceleration response of lining structure and slope increases significantly,it shows that the tracking nature of the acceleration of lining structure response to the acceleration of surrounding rock;The influence of the height of the entry elevation on the acceleration response of lining structure is closely related to the amplitude of excitation amplitude,at the foot slope height into the tunnel's acceleration response is much less than the 1/2 times slope height into the tunnel's lining structure.The height of the tunnel elevation has a significant amplification effect on the acceleration response of the tunnel lining under the high intensity earthquake,the results of monitoring data and the location of the earthquake damage of the model are verified each other.(5)Based on the three-dimensional finite element model of Midas-GTS,the dynamic response of the tunnel lining structure under the two conditions of at the foot slope height into the tunnel and 1/2 times slope height is compared and analyzed,presented the anti-seismic fortified length of loess tunnel portal section,it is considered that the influence of the entrance elevation of the tunnel on the seismic wave amplification effect should be taken into account when the hole diameter is 8 times higher than that of the hole,and the entrance elevation of the tunnel on slope has no significant influence on the acceleration response of the lining after more than 8 times the tunnel diameter. |
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