| With the continuous enhancement of China's economic strength,and the implementation of a series of new strategic measures,the western region has ushered in a major opportunity.A large number of high speed rail lines are being built in the western region,and a large number of high speed lines are being or have been planned in the coming fifteen planning Midwestern Sectional Figure Skating Championships.In the west of China,there are high mountains and valleys,and the terrain is complicated.In the process of building high-speed railway,a large number of tunnels need to be built to cross the mountains.therefore,it is very important to study the dynamic response of the high and steep slope at the entrance of the Loess Tunnel.Based on the Wangjiagou Loess Tunnel Project of Baolan Passenger Dedicated Line,With the aid of Midas GTS NX finite element software and shaking table model test,the dynamic response characteristics of the high steep slope at the entrance of the Loess Tunnel are studied,the results showed that:(1)It is found that the slope displacement increases with the increase of the tunnel entrance elevation by numerical simulation,while the acceleration decreases with the increase of the tunnel entrance elevation.The maximum displacement and acceleration respectively are 20.26cm and 9.92m/s~2 when the entrance site locates at slope foot.They change to21.13cm and 9.27m/s~2 when the entrance height is one third elevation,while the two third elevation they are 36.74cm and 8.38m/s~2.(2)The failure process of the model can be divided into three stages by observing it's failure phenomenon.The test model changes little in the early stage of 1 to 9 working conditions.In the middle stage of 10 to 18 working conditions,the number of cracks on the top and the side increased,the width of the cracks increased,and they extended to the lower part of the model accompanied by the peeling off of a large amount of soil.During the later stage of 19 to 29 working conditions,the crack at the top continued to expand and tilted towards the upward slope.Finally,the model was completely destroyed after an"S"sliding generated on the upward slope.(3)The peak acceleration of each point in the inner model gradually increases with the loading conditions.The peak acceleration on the slope surface gradually increases with the increase of the height of the slope,and the maximum value whose figure is 15.8m/s~2 locates at the surface point of A25.The maximum peak acceleration of tunnel lining is in the range of 0?60m near the entrance of the tunnel.The maximum peak acceleration and PGA amplification factor appear at the tunnel vault A18 and the tunnel back arch A7.the acceleration curve and Fourier curve both gradually increase with the increase of the elevation,and amplitude of accelerations whose maximum values appear at the top of the slope in the X direction is larger than it in the Z direction.(4)The maximum principal stress and shear stress of the tunnel lining both decrease in a wave shape with the increase of the distance from the tunnel axial direction to the tunnel entrance.The maximum shear stress values of the tunnel lining are greater than the maximum principal stress of the tunnel lining.the maximum principal stress value 9.5MPa appears at the vault in loading condition 18,and the maximum shear stress value 14.4MPa which is about1.5 times of the maximum principal stress value appears at the same position.Both the maximum principal stress value and the maximum shear stress value appear in the range of 0?60m near the tunnel entrance.The earth pressure value increases with the distance from the tunnel entrance,and they gradually increases with the continuous loading of the working conditions whether at the vault or the arch.For the same section,the earth pressure at the arch is larger than that of the tunnel vault,which is about 1.3 times that of the vault.(5)The results shows that the slope acceleration,tunnel lining acceleration,and maximum principal stress of the tunnel lining obtained from model tests and numerical simulation are basically same,indicating that the parameters and research methods selected are reasonable and effective.The research results have some significance to guide the tunnel design and construction in the aspect of earthquake resistance. |
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