The Study On Seismic Dynamic Response Characteristics For Portal Section Of Loess Tunnel In Bridge-tunnel Connection Engineering

As a complex combination structure of bridges,tunnel structures and surrounding rock on the side slope of the tunnel,the bridge and tunnel connection project can well meet the complex terrain of steep terrain and mountain valleys,which has attracted extensive attention at home and abroad,especially in China.There are many applications in the western mountainous areas.According to the China Seismological Network Center,China is still in the active period of strong earthquakes of magnitude 7,while the main areas of the earthquake are still in the northwest and southwest of China,especially since the 2008 Wenchuan earthquake,the surrounding seismic activity continues to spread.Under the action of earthquakes,the earthquake damage and secondary disasters in the tunnel entrance frequently occur frequently being like a throat.and the seismic design of the tunnel section has become the most important.The loess area in the loess area of western China is very developed,the surface is relatively broken,and the loess slope often has a steep slope.Based on the complex engineering geological conditions and the active and active earthquakes in the loess area,the tunnel project in this area is more susceptible to earthquakes.In addition,the tunnel entry location in the bridge-tunnel connection structure is often on the hillside,which is quite different from the traditional tunnel from the slope foot.However,due to the relatively backward development of seismic theory of underground structures,the seismic prototype data is relatively lacking.There have been few reports on the seismic dynamic characteristics of the bridge-tunnel connected structures.In response to the above problems,this paper relies on the National Natural Science Foundation project(41562013)“Research on the dynamic response characteristics and seismic technology of the loess tunnel opening section considering the elevation of the slope into the tunnel”,combined with the actual project of Baolan Passenger Special,through finite element numerical calculation and large-scale vibration.The model test conducted a systematic study on the seismic dynamic response characteristics and anti-shock absorption of the tunnel section of the loess tunnel in the bridge-to-building project.The main research work and achievements are as follows:(1)The research method and current situation of tunnel seismic response are expounded.On the basis of discussing the seismic fortification measures and the application of bridge and tunnel connection engineering,the influencing factors of disease damage and safety hazards of bridge and tunnel connection engineering are analyzed.The types of earthquake damage and the characteristics of the tunnels in the bridge and tunnel connection project.(2)The finite element analysis software Midas GTS/NX was used to analyze the dynamic response characteristics of the slope and lining structure displacement,accelerationand principal stress of the bridge-tunnel connected structure under earthquake action.The research shows that the slope displacement and acceleration response show a certain amplification response along the slope height and reach saturation near the slope top.The loess slope will eventually produce a curved slip surface along the slope height and produce a layer on the slope.Horizontal cracking;the dynamic response of the tunnel lining is inversely related to the axial distance of the hole,and the main area of the dynamic response is 5 times the hole from the opening.the bridge-to-pipe connection structure will affect the distribution of the ground motion response of the tunnel opening and cause The stress concentration phenomenon occurs at the top of the tunnel entrance arch,but it does not change the development trend of the tunnel lining acceleration,displacement and principal stress with the hole distance.(3)On the basis of studying the similarity theory and boundary conditions,the design process of the shaking table model test is analyzed,and the material ratio and physical property parameters of the model test are determined through a series of laboratory tests,and the model structure required for the test is developed.Design the layout of the measuring points,select the seismic wave and loading scheme,and successfully complete the large-scale shaking table model test.After analyzing the whole process of the bridge-tunnel connection structure in the shaking table test,the seismic dynamic response characteristics and its variation law of the tunnel section of the loess tunnel are studied in detail.The boundary effect of the slope top is discussed.The influence of response,and the vertical acceleration acceleration can be used as the judgment basis for the start of the vibration table model.By analyzing the seismic wave holding time and the spectral characteristics,it is shown that the slope of the tunnel cavity is close to its excellent frequency and the low frequency seismic wave is amplified within 20 Hz.The effect is to filter the high-frequency wave greater than20Hz;the seismic wave duration of the acceleration peak is 18s~30s,and the seismic wave duration is mainly related to the seismic wave intensity,but not directly related to the seismic wave loading mode and the surrounding rock position.The time required for the slope acceleration peak in each direction tends to be smaller and smaller as it tends to break.(4)Combining the model test and simulation calculation results,the interaction and failure mechanism of the bridge-tunnel-slope in the tunnel section are studied.According to the anti-shock technology requirements of the tunnel,the loess in the bridge and tunnel connection project is proposed.The seismic fortification length and protection points of the tunnel entrance section.