Study On Seismic Dynamic Response Characteristics And Response Spectrum Of Loess Slope-tunnel Structure

With the rapid development of China's economy,the state has invested more and more in the transportation infrastructure projects in northwest China,such as the Zhengzhou-Xi'an Passenger Dedicated Line,Baoji Lanzhou passenger dedicated line,Lanzhou Chongqing railway,Chengdu Lanzhou railway,Yinxi railway,etc.The construction of these projects must pass through the loess area.The special geological and geomorphic characteristics and strong seismic background in the loess area bring many complicated scientific and technological problems to the construction and operation of traffic engineering.Therefore,it is very important to study the dynamic response characteristics and seismic performance of tunnels in the Loess area under seismic action,especially with the active tectonics and earthquakes gradually active in the west of China in recent years,the study on the stability of the Loess Tunnel under strong earthquake motion is of great significance to the overall smooth of the transport engineering and the rapid rehabilitation after the earthquake.In this paper,through the large-scale shaking table model test,the seismic dynamic response of Loess Tunnel on slope is studied,and the response spectrum and spectral ratio of slope-tunnel structure in different directions are studied.The main research contents and conclusions are as follows:(1)Consult domestic and foreign literature on the dynamic response characteristics of the slope-tunnel structure under the action of earthquake,and the response spectrum and spectrum ratio of the ground motion intensity.Through sorting and categorizing,this paper summarizes the research methods of tunnel earthquake resistance,the mechanism analysis of tunnel earthquake damage,the research and application of acceleration response spectrum and spectrum ratio,and determines the research content of this paper according to the latest research results.(2)Based on the similarity theory,the similar parameters of similar materials of surrounding rock were obtained,and the filling of tunnel model was completed and large-scale shaking table model test was carried out.The field image data of the model test were obtained under different loading directions and different seismic wave input,and it was concluded that the model was in the elastic stage from 1 to 7,the elastic-plastic stage from 8 to 12,and the failure stage from 13 and 14.(3)Under different waveforms and different loading directions,the peak acceleration of each monitoring point varies with the elevation and the depth of the tunnel.The existence of the tunnel inhibits the peak acceleration of the surrounding slope,and the tunnel portal is the weak point of seismic resistance.Under the unidirectional loading of different intensities,the horizontal peak acceleration amplification coefficient has the same change rule,which is similar to a straight line,and the vertical peak acceleration amplification coefficient shows a zigzag change.Under bi-directional loading,the amplification coefficient of the horizontal peak acceleration has the opposite tendency to that of the vertical peak acceleration,and the amplification coefficient is much smaller than that under unidirectional loading.The peak acceleration under the loading of Wenchuan Tangyu wave is concentrated around 42 s,and El Centro wave is concentrated around 21 s.(4)Introducing the strength of Arias to reflect the energy level of the ground motion.By drawing the energy profile of the longitudinal section to determine the deformation process inside the model,it is concluded that the elastic-plastic phase and the failure phase of the model are advanced relative to the image data,indicating that the deformation and failure in the model will be prior to the appearance of the model.Under unidirectional loading,the soil in the model has both an energy-enhancing and attenuation areas.Under bidirectional loading,the enhancement or attenuation has a great relationship with the waveform.(5)Under different ground motion input,the response spectrum and spectral ratio of the slope-tunnel structure under different working conditions are studied.The results show that the acceleration response spectrum first increases and then decreases with the increase of period under different working conditions,and finally approaches to zero,with prominent peaks.The maximum value of the average acceleration response spectrum increases with the increase of the ground motion input,and the average response spectrum of horizontal acceleration is larger than that of vertical acceleration.The curve shape of the average response spectrum ratio of acceleration is similar in the short period,but the variation rule is inconsistent in the middle and long period.In the short period,the average normalized response spectrum decreases with the increase of ground motion,and in the middle and long period,it increases with the increase of ground motion.The peak value of the average normalized response spectrum tends to move to the middle and long period with the increase of ground motion.In the short period,the change rule of the average normalized response spectrum ratio is the same,in the middle and long period,the change rule is not the same.In the short period,the vertical average normalized response spectrum is greater than the horizontal,in the middle and long period,the horizontal average normalized response spectrum is greater than the vertical average normalized response spectrum.