Analysis Of Dynamic Response And Reasonable Distance Of Samll Clear Distance Tunnel Under The Action Of Earthquake

With the rapid development of the economy,the number of tunnels has increased continuously.However,in many areas,due to the limit of topographical geological conditions or special bridge and tunnel connections,the distance between the two ordinary tunnels meet the demand no longer.As a result,a new form of tunnels with small clear distance has emerged.At the same time,Earthquakes happen frequently in China,a considerable number of tunnels are subject to earthquakes,which located in high-intensity seismic regions.At present,with regard to seismic analysis of the underground structures and the study on construction mechanics,there is less research on the samll clear distance tunnel under earthquake.Therefore,the static calculation of 80 working conditions and the dynamic calculation of 80 working conditions are performed for samll clear distance tunnel using ANSYS,the dynamic response and reasonable distance of samll clear distance tunnel under earthquake were analysed and discussed in this thesis,the main contents and conclusions are as follows:(1)The seismic characteristics of underground structures were briefly described.The research status of seismic resistance of the samll cleardistance tunnels was summarized,and the seismic analysis methods and research progress of general underground structures were introduced.(2)Some key issues of numerical simulation such as artificial boundary condition,seismic wave input program are proved by numerical examples,their solution efficiency and calculation precision are both satisfied.(3)Some samll clear distance tunnel models under different conditions were established.Taking the 1.17 B net distance under the condition of grade IV surrounding rock as an example(B is the hole width of a single tunnel).It is concluded that the tunnel under the static conditions,the greater the equivalent stress on both sides of the arch waist,the plastic strain on both sides of the arch feet.Before and after the supported,it is found that the supported structure has a good effect on the stress and strain of the surrounding rock.(4)The modal responses of grade II,III,and IV surrounding rocks,0.36 B,0.63 B,0.90 B,1.17 B,1.44 B,1.71 B,and 2.25 B are calculated,for determining the damping used by dynamic analysis.The laws of displacement,acceleration,equivalent stress and equivalent plastic strain of grade II,III and IV surrounding rock at 1.17 B were studied.As the grade of surrounding rock decreases,the displacement of the surrounding rock increases significantly.The worse the surrounding rock quality,the greater the change of above.Comparing the results of displacement,acceleration,equivalent stress and equivalent plastic strain of grade III surrounding rock under the different PGA(0.1g,0.2g and 0.4g),as PGA increases,the dynamic response at each point increases,and the acceleration magnification decreases gradually.(5)According to the calculation of the dynamic about different surrounding rocks,different supporting conditions and different PGA,considering the law of displacement and equivalent stress changes,the study shows that the minimum reasonable distance of the samll clear distance tunnel of grade II surrounding rock is 0.63 B under unsupported conditions;the minimumreasonable distance of grade III surrounding rock under the conditions of being supported and unsupported is 0.90 B and 1.17 B respectively.The minimum reasonable distance of grade IV surrounding rocks in supporting and unsupported are 1.44 B and 1.71 B respectively.The minimum reasonable distance are 0.90 B,1.17 B,and 1.71 B for the samll clear distance tunnel after being supported of grade III surrounding rock under the PGA of 0.1g,0.2g,and0.4g,and the grade IV surrounding rock are 1.44 B,1.71 B and 1.98 B respectively.The results show that the minimum reasonable distance is reduced,for which the samll clear distance tunnel after supported.Also,the poorer the surrounding rock mass it is,the bigger the minimum reasonable distance is.The greater the ground motion intensity it is,the bigger the minimum reasonable distance is.In conclusion,in the aspects of displacement,stress and strain,the dynamic response of the small clear distance tunnel under the action of earthquake is much larger than that under static condition.It is recommended to ensure the stability of a small clear distance tunnel during the design and construction of the small clear distance tunnel,appropriate measures of support should be taken,especially for the parts of the internal arch waist,arch feet and middle rock,which has a large part of force and deformation.The minimum reasonable distance of the small clear distance tunnel is affected by the surrounding rock,the support and the PGA conditions.The dynamic response of the small clear distance tunnel under the action of earthquake has a great value and space of the research still.