| Since the 21 st century,with China’s increasing investment in infrastructure in the northwest region,the policy of the Belt and Road has been continuously promoted,and large-scale railways,highways,and subway tunnels have been built.Many railway traffic safety issues have become increasingly prominent and need to be resolved.The mountains in the northwestern part of China are mostly,and the soil is mostly collapsible loess.Therefore,when crossing the loess tunnel for railway construction,it has encountered enormous challenges and difficulties.Due to the high frequency of earthquakes in China,and the tunnel portal section is the key location for earthquake resistance,the foundation failure and structural damage are more likely to occur.It is also relatively rare.Therefore,it is of great significance to carry out research on the deformation and failure laws and dynamic response of tunnel portal sections in the loess area under earthquake action.In this paper,large-scale shaking table model test and finite element numerical simulation are used to study the seismic dynamic response of the tunnel section of the loess tunnel.The seismic impact of the incident direction of the seismic wave on the tunnel portal section is considered,and the tunnel elevation is taken as a key parameter.The model of the slope tunnel system with the slope of the slope at 60° and the slope foot into the hole is emphasized.It provides a useful theoretical basis for the selection of mountain tunnels and the selection of anti-shock measures for the tunnel entrance.The main research contents and conclusions are as follows:(1)In this paper,the related tunnel seismic damage and anti-shock absorption data are summarized,and the development history of the tunnel,the seismic design method and the influencing factors of the tunnel entrance are summarized,concisely and concisely put forward the research content and research ideas of the thesis.(2)According to the research content,experimental conditions and related ideas,a large-scale shaking table test model of tunnel opening section with a similar ratio of 1:80 was designed.The slope of the slope was 60°,and the bottom of the slope was used to analyze the acceleration of the model under different loading conditions.Displacement,pressure and shear stress.The existence of the tunnel has a certain inhibitory effect on the acceleration of the surrounding slope.The peak acceleration of the slope shows an overall increasing trend with the increase of the slope height,showing a slope enlargement effect.The peak acceleration of each point of the tunnel lining decreases with the increase of the hole and tends to be stable,showing a certain hole enlargement effect.The slope displacement has a certain cumulative effect.As the seismic intensity increases,especially near the hole,the displacement spreads to the top of the slope.(3)Based on the MIDAS GTS/NX three-dimensional finite element numerical simulation,three different models of entry elevation are compared and analyzed,namely,foot-slope entry,1/3-fold-slope-height entry and 2/3-fold-slope-height entry.The results show that the acceleration of slope increases with the increase of slope gradient,showing a positive correlation.At 80 m near the top of the slope,the slope acceleration tends to be stable to a certain extent,showing a certain acceleration saturation effect.Therefore,the dynamic response of the upper and middle slopes is stronger in different tunneling modes,and it can be used as a key fortification.(4)The dynamic response characteristics of seismic waves in the three different directions of the input level x,y and vertical z to the tunnel entrance and slope are studied respectively.The results show that the acceleration and displacement of the slope are different under different seismic directions.In general,the horizontal y direction parallel to the tunnel axis is the most unfavorable incident direction,and the damage to the tunnel and the side elevation slope is stronger.It provides a reference for the seismic design of the actual engineering portal section. |
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