Research On Anti-shock Technology Of Shallow-buried Section Of Extra Large Section Highway Tunnel Under High Intensity Earthquake Condition

China is an earthquake-prone country and its seismic activity is characterized by high intensity,high frequency and shallow source.As the infrastructure of the traffic and the throat hub,the tunnel will become a hindrance to the lifeline of the disaster relief once it breaks down in the strong earthquake.In addition,with the improvement of the grade of the new road,the tunnel section has a tendency to become extraordinarily developed.Therefore,in the high-intensity fortification area,the research on the dynamic response and anti-shock reduction measures of the super-large section highway tunnel has important engineering and practical significance.This paper combines the schoolenterprise cooperation scientific research project to carry out the following research on the shallow-buried section of the super-large section highway tunnel under high-intensity earthquake conditions,aiming to provide some reference and supplement for the seismic and shock absorption of the mountain tunnel.Firstly,on the basis of collating and collecting a large number of typical tunnel seismic damage data,the typical damage modes of tunnels are summarized,and the main disaster-causing mechanism and its influencing factors of shallow tunnels are analyzed.The common methods for seismic dynamic response analysis of tunnels are summarized..Then,the basic method of seismic dynamic finite difference analysis is briefly described.The realization of dynamic artificial boundary and mechanical damping in FLAC3D is clarified.The selection,filtering and correction methods of seismic waves under high intensity conditions are studied.On this basis,this paper relies on the Qujing Sanbao to Kunming Qingshui high-speed Xiangyangshan tunnel project to analyze the seismic dynamic response and anti-shock measures of the shallow-buried section of the superlarge section highway tunnel through FLAC3D finite difference software:the main contents and results are as follows:(1)The dynamic response law of different depths of the tunnel body section in the shallow buried area is analyzed.It is concluded that the acceleration and displacement peaks decrease gradually with the increase of the buried depth,while the stress peak increases first and then decreases slightly to The gradual stability is compared.The dynamic response characteristics of the shallow-buried tunnel section and the largesection tunnel of the super-large section tunnel are compared and analyzed.The calculation results show that the peak response of the arched waist and the side wall is more concentrated due to the flattening of the section.(2)Comparing the seismic dynamic response of the tunnel shallow tunnel section at three different slope angles,the peak distribution of the tunnel section is obtained.It is found that the tunnel lining reacts under strong earthquake when the slope angle is large.The more unfavorable.The variation of the depth of the displacement value is not affected by the slope angle of the ascending slope.(3)By controlling the single variable modeling and analysis,a damping layer is set between the initial branch of the tunnel and the second lining.It is found that the shock absorbing layer has a significant influence on the peak response of the tunnel structure,and a reasonable damping layer material and thickness are obtained.A series of studies on grouting and strengthening surrounding rock shows that deep full-circle grouting is the best grouting method,and the reasonable grouting interval between grouting layer and surrounding rock is lm,and the reasonable range of grouting layer thickness is 4～5m.(4)Comparing the seismic dynamic response of the shallow buried tunnel section in three different spacing seismic joints,it is found that the stress response peak of the seismic joint is improved obviously,and the seismic effect of 10m spacing is the best.