Study On The Influence Of Void Defects On The Safety Of High-speed Railway Tunnels Under Static And Dynamic Loading

With the rapid development of high-speed railway tunnels in China,a large number of tunnels have been built and put into use.Due to the problems of complex geology and low construction quality,some quality defects exist in the tunnels.Based on the actual project of Tongyu Railway,this paper uses the numerical analysis method in view of the situation that the vault of the railway line is empty.The internal force distribution of tunnel lining under static conditions and dynamic response law of tunnel lining under train load when the vault is vacated in different degrees are analyzed,and the safety of tunnel lining is judged according to the calculation results.The main research results are as follows:(1)According to the statistics of 22 tunnels on copper-jade railway,it is found that void,arch and side wall are 2.88% and 3.77% of the total defects respectively,and the main location of void and side wall defects is the vault.Although the number of cavity defects accounted for a low proportion of the total defects,but the harm is greater.The damage caused by cavitation is not single,but mutual,mainly for the destruction of lining and surrounding rock support,leading to cracking and peeling of lining,and inducing other lining damage.(2)The void of the lining vault changes the stress state of the lining,and the inner tensile force of the vault changes from the outer tensile force to the inner tensile force when there is no void,and the tensile stress value is large.At the same time,the lining of the void part extrudes outward,which is not beneficial to the safety of the structure.The change of cavitation Angle significantly affects the safety of lining structure.When the length of the void changes,the sections in the unfavorable state will increase,which will affect the safety of the structure.The effect of clearance height on lining stress is less than that of clearance Angle and length.(3)The vibration force of the train causes the tunnel lining to vibrate.The intensity of the vibration response decreases with the increase of the distance from the vibration source,and the dynamic response of the tunnel lining is more obvious below the shoulder.When the vault is void,the displacement,velocity,acceleration and dynamic stress of the vault increase in different degrees under different vehicle speeds compared with that without void,but the increment is small.The dynamic response of the lining vault is affected significantly by different vaults.When the vaults are larger than 30°,the growth range of velocity,acceleration and dynamic stress increases significantly.When the clearance Angle is 50°,the displacement of the vault is 0.385 mm and the velocity is 4.39mm/s,which are close to the allowable value of vibration safety,so attention should be paid to it.The dynamic response of lining vaults is not affected by different voiding heights.(4)When the circumferential void of 30° exists in the vault,and the train runs 20round-trip trains every day for calculation when the speed of the train is 300km/h,the fatigue life of the lining vault cannot meet the design requirements of 100 years.In order to improve the service life of the high-speed railway,tunnel monitoring should be strengthened and the regulation effect should be improved.The occurrence of the cavity behind the lining does not directly damage the lining,but by changing the contact state between the surrounding rock and the lining,it causes the deformation and peeling of the surrounding rock,the local deformation of the lining increases,and the stress concentration results in the crack damage of the lining.The treatment should be carried out according to the failure mechanism and form of lining and the actual situation.