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DYNAMIC BEHAVIOR OF PORTAL PART OF TRAFFIC TUNNEL IN HIGH-INTENSITY EARTHQUAKE AREA交通隧道在高烈度地震区洞口动态行为探究外文翻译专业名称：土木工程年级班级：道桥08-4班学生姓名：张 银指引教师：徐 平河南理工大学土木工程学院二一二年六月十一日DYNAMIC BEHAVIOR OF PORTAL PART OF TRAFFIC TUNNEL IN HIGH-INTENSITY EARTHQUAKE AREASHEN Yusheng1,2 ,GAO Bo2 ,WANG Zhengzheng2 ,WANG Yingxue21Postdoctoral Station of Mechanics，Southwest Jiaotong University，Chengdu 610031，China；email:. 2School of Civil Engineering,Southwest Jiaotong University，Chengdu 610031，China；Abstract：A large-scale shaking table test is accomplished on the dynamic response and failure modes of the tunnel. The result is that the largest dynamic response of tunnel structure appears at the side-wall and the shear or fracturing damage appears at the invert，which is basically the same damage state with tunnel engineering in 5.12 Wen Chuan earthquake. The internal force value of tunnel structure minish and the numbers of cracks reduce after the shock absorption layer is set up in model test，and optimize the stress state of tunnel. The surface cracks of tunnel model appear firstly at both spandrels and develop diagonally at the tunnel entrance. The cracks arise X-shape distribution on the surface of the model soil. There are a lot of circumferential cracks at tunnel portal under the condition of dynamic loads，and most of longitudinal cracks or oblique cracks can terminate when extending to the circumferential cracks. So that it is proposed that there should be designed more shock absorption seams in the vicinity of tunnel portal in order to be propitious to damping the earthquake energy. Key words：dynamic behavior，shaking table test，high-intensity earthquake area1 Introduction It is regrettable that the peoples lives and property have suffered great losses during 5 12 Wenchuan earthquake in Sichuan province. At the same time the civil transport engineering are damaged to some extent，including the tunnel engineering. Tunnel damage survey shows that the tunnel portal section is the most easily to destroy and is the most weak parts(Li,). Especially at the high-intensity earthquake area，the stability analysis of the tunnel entrance，portal and side slope will be focused on in the field of the anti-seismic technology research. The mechanical characteristic of tunnel lining is a considerably complex process，the grade of surrounding rock is various and there are a variety of non-linear features(Luo,). It is a effective way to research the tunnel anti-seismic characteristic by the shaking table test in the earthquake engineering field because the establishment of non-linear equations of motion and the numerical solution is still not perfect(Chen,；Gong,；Yang，；Zhou，). It is inevitable to encounter any problems that the tunnel projects could be possible to adopted in the vicinity of the fault or high-intensity earthquake area during the construction of the traffic engineering in Western China regions (in particular the South-West). The line from Yaan to Lugu highway is across the seismic faults several times (Xianshui River fault zone and Anning River fault zone) and the seismic fortification intensity is from degrees to degrees，in particularly degrees at local regions. The peak acceleration of ground motion is from 0.15g 0.4g，which parameters are the relative large in the current construction of the highway. In this paper，the dynamic characteristics of tunnel structure is analyzed at the mountain tunnel portal according to the actual engineering，thus the law of stress-strain and failure mode of the tunnel and surrounding rock are researched under the ground motion load，which provides an important reference for the design and construction of the highway tunnel in high-intensity earthquake area.2 Relying on engineering conditions and shaking table test device 2.1 Geological conditions Model test was accomplished in august ，based on certain tunnel project where there is through the region of seismic fortification intensity degrees and may be active faults in Ya-Lu highway. Based on drilling and surface survey，the tunnel stratum is mostly triassic systemJurassic system，silty mudstone，pelitic siltstone，quartz sandstone，carbargillite，Cenozoic overlying Holocene Quaternary cover. 2.2 Shaking table test The shaking table at the Traction Power State Key Laboratory is the main facility for experimental research into earthquake engineering at Southwest Jiaotong University. The model test adopts the bi-directional seismic shake table，which table size is 2.5 m by 2.5 m，the platform capable of carrying a maximum payload of 30t and the vibration mode is for X，Y two direction and four freedom degrees. The frequency range is 0.1 30 Hz，and the peak acceleration of X or Y direction is 1.0g respectively. It is driven horizontally and vertically by four 20kN servo actuators giving full control of motion of the platform in 4 DOF simultaneously. 3 Design of model test similar parameters Taking into account the model border effect，the width of the box model should be more than 6 times the tunnel width，thus the similar parameters are determined(geometry similar CL =30，Youngs modulus CE = 45，density C =1.5) and Shen () described the rest of physical similar parameters. 3.1 Design of similar material for surrounding rock and secondary lining According to the similar relation and the physico-mechanical parameters of surrounding rock in situ，the similar material selected is consisted of flyash，river sand and oil after the orthogonal tests are repeated dozens of times. At last these similar material will be mixed according to a certain similar ratio.The secondary lining material selected is consisted of plaster，quartz sand，barite，water by a certain percentage of preparation，which mechanical parameters are shown in Table. 1. Table.1 Mechanical parameters of concrete similar materialparametersDesign valueTheory valueTest valueSimilitude relation (kN/m3)2516.717.0reasonableE(MPa)29.50.660.72reasonablec (MPa)12.50.30.426approximately4 Test measurement and scheme 4.1 Strain measurement of tunnel structureStrain gauges are firstly arranged for the tunnel site where the internal force and deformation of tunnel is maximal. The sensor wire should be firmly fixed at the surface of the model structure and fetched out from the certain position where the model displacement is lesser at that direction. The schematic diagram of measurement points are laid in Figure.1 in order to verify the dynamic response law of tunnel structure. Figure.1 Layout scheme of sensors Figure.2 Accelerations time-histories curve4.2 Test load -earthquake wave The earthquake waves adopted is the artificial wave that is synthesized by the Sichuan Seismological Bureau under the conditions of the site response spectrum synthesis in model test. The exceedance probability of earthquake waves is2% ，the original peak acceleration is 0.67g，the hold time is about 20s in the part of strong shock，most of the earthquake waves Energy is less than 15s and is within 15Hz in the frequency (in Figure. 2). 4.3 Test scheme In Table.2，the case 2 and 3 are to study the effect of the shock absorption layer. The polyethylene material that is adopted to the shock absorption layer circumfuses the outside surface of the tunnel lining (the invert is not laid). Table.2 Test conditions of mountain tunnel modelnumbercaseremark1single-tunnel portalvalidating the anti-seismic characteristic of single-tunnel 2bi-tunnel portalbi-tunnel have not shock absorption measure3bi-tunnel portalsingle-tunnel has shock absorption measure5 Model test results and analysis 5.1 Strain response analysis of tunnel structure There are more than 30 strain gauges at the key positions，thus the strain response law of the tunnel lining is obtained by the strain gauges. In Figure.3，when the acceleration 0.4g(equivalent to degrees) is input from shaking table，the maximum strain amplitude value of the vault is 22 in the case 2，while the case 3 is for 6.5，thus the strain amplitude value is obviously decreased after the shock absorption measure is taken. The maximum strain amplitude value of the invert do not change because the shock absorption layer is not set at the right tunnel invert. So it is obvious for the damping effect that the shock absorption measures are taken for tunnel structure at the tunnel portal. a) Strain curve of vault in case 2. b) Strain curve of invert in case 2. c) Strain curve of vault in case 3. d) Strain curve of invert in case 3.Figure.3 Time-histories of strain at different points of right-tunnel( a=0.4g)The structural strain values recorded from various measuring points do not tend to be zero after the vibration is over，which phenomenon is mainly due to the rock and soil producing permanent deformation around the tunnel structure under the condition of the dynamic loading，so that the additional seismic strains occur on tunnel structure5.2 Patterns of damage of model test comparative analysis There are various cracks on the surface of the similitude material in both cases，but those cracks of tunnel model appear firstly on both spandrels and then develop diagonally. In Figure. 4a，the cracks arise X-shape distribution on the surface of the model soil and the model soil cracks of right tunnel are more than left tunnel at the surface of tunnel. There is a 45 angle between the direction of cracks and the tunnel longitudinal direction，the numbers of cracks in right tunnel close to the side of border are less than the other side and there appear a lot of run-through cracks on the surface of the model soil due to small distance of both tunnels. a) case2 (no shock absorption layer) b) case3 (shock absorption layer)Figure.4 Failure modes on the surface of tunnel model materialIn Figure. 4b，there is less cracks on the surface of model soil after the shock orption layer is set up at right tunnel，which weakens the interaction between the model soil and tunnel structure. It is obviously effect that a certain thickness shock absorption layer is designed at the mountain tunnel portal，at the same time it is proposed that the slope of tunnel portal should be reinforced in order to prevent the secondary disasters(such as landslide，slope instability，etc) due to earthquake.5.3 Contrast or analysis of failure modes in tunnel structure In Figure. 5，the tunnel structure appears a number of longitudinal cracks，diagonal cracks and shear cracks at the foot of side-wall with the increasing seismic loads，because the shock absorption layer is not designed at tunnel portal in case 2. But in case 3，the overall tunnel structure is not apparently damage，only are there less micro-cracks at local position of tunnel structure and the tunnel invert arises damage or destruction. When the stiffness of the tunnel portal structure is much larger than the strata stiffness，the surrounding rock displacement could have made underground structure forced deformation while happening earthquake，at the same time the earthquake inertia force obviously intensify at the tunnel portal，which results in tunnel structure to appear cracks. The model soil and model structure could be easily to appear shear or tensile destruction at tunnel portal under the action of both surrounding rock displacement and earthquake inertia force. a)Case2 (without shock absorption layer) b)Case3 (shock absorption layer)Figure.5 Failure modes of tunnel modelThere are a lot of circumferential cracks at tunnel portal，where the numbers of cracks are more than others position，as well as most of longitudinal cracks or diagonal cracks can terminate when extending to the circumferential cracks. So that it is proposed that there should be set up more shock absorption seams in the vicinity of tunnel portal in order to be propitious to damping the earthquake energy. Shaking table model test shows that the tunnel damage position concentrates on the tunnel portal，which damage state is the same with the tunnel engineering damage in “Sichuan 5.12 Wenchuan earthquake”. Zhe hu shan tunnel occurred several times landslide and structure destruction during the Wenchuan earthquake and its aftershocks，which bring greater traffic obstacles for the rescue and disaster relief under the common effects secondary disasters and damage of the tunnel structure itself at tunnel portal. 6 Conclusions Here we may draw the following conclusions. (1) According to the tunnel internal force changes and failure modes，the largest dynamic response of tunnel structure appears at the side-wall and the shear or fracturing damage appears at the invert，which damage state is basically the same with tunnel engineering damage in 5.12 Wen Chuan earthquake. So that this model test is reliable.(2) The internal force value of tunnel structure minish and the numbers of cracks reduce after the shock absorption layer is set up in model test，at the same time it can greatly reduce the earthquake destruction and optimize the stress state of tunnel. So it is provide a certain reference for the anti-seismic design and construction of mountain tunnel in high-intensity earthquake area. (3) The surface cracks of tunnel model appear firstly on both spandrels and develop diagonally in tunnel entrance. The cracks arise X-shape distribution on the surface of the model soil，at the same time it is proposed that the slope of tunnel portal should be reinforced in order to prevent the secondary disasters(such as landslide，slope instability，etc) due to earthquake(4) There are a lot of circumferential cracks at tunnel portal under the condition of dynamic loads，and most of longitudinal cracks or oblique cracks can terminate when extending to the circumferential cracks. So that it is proposed that there should be set up more shock absorption seams in the vicinity of tunnel portal in order to be propitious to damping the earthquake energy.Acknowledgements This study is funded by the Postdoctoral foundation of China (No.0431267)，the National Natural Science Foundation of China(No.50878187) and the Foundation of Southwest Jiaotong University(No. B19)References Chen，G. X. (). A large-scale shaking table test for dynamic soil-metro tunnel interaction test scheme. Earthquake engineering and engineering vibration，26(6):178 183. Gong，B. N. (). Experimental Research on Dynamic Interaction of Underground Structure and SoilJ. Journal of China Three Gorges Univ，(6):493496. Li，Y. S. (). Study on earthquake responses and vibration-absorption measures for mountain tunnel. Shanghai：Tongji University. Luo，D. L. (). Researchon Simulating Material of Surrounding Rock in Tunnel Seismic Model Experiment， Journalof Shijiazhua