Study On Safety Evaluation And Treatment Measures Of Cavity Defects Behind Railway Tunnel Lining

Along with the rapid development of railway tunnels in China,the diseases of tunnels are becoming more and more obvious.Among them,the cavity disease behind tunnel lining is one of the main diseases that affect the healthy service and safety of tunnel lining structures.At present,the research on the cavity behind the tunnel lining is mainly focused on the stress state and disposal measures of the lining structure with the cavity.However,there are relatively few researches on the safety evolution law,evaluation method and standard of the tunnel lining structure with holes.Based on literature review,tunnel site investigation,finite element numerical analysis and representative work site disease remediation,this paper systematically studies the lining lining structure’s stress characteristics,safety status and tunnel lining condition evaluation in view of the factors and genetic mechanism behind the tunnel lining cavity disease and its genetic mechanism,different cavity sizes and different cavity positions.The main research contents and conclusions are as follows:(1)This paper investigates the characteristics and distribution of cavity defects behind the tunnel lining,and concludes that the cavitys mostly occur in the vault position,and the arch waist and arch wall parts are relatively less.The reasons for the formation of the cavity defects are analyzed,mainly due to the coMPlex geological conditions of the tunnel crossing area,the iMProper control of construction quality and the limitation of construction equipment and so on.(2)In this paper,the Midas GTS NX finite element software is used to establish the cavity defect model behind the tunnel lining,and the force of the tunnel lining under different working conditions is simulated and analyzed,the results show that;(1)The existence of cavity defects behind the lining causes the lining structure to develop in an unfavorable direction.Especially,the lining structure near the cavity position changes greatly,and the axial force and bending moment increase with the increase of the cavity.For exaMPle,under the condition of grade IV surrounding rock,the width of cavitys is 0.5m and the depth of radial cavity increases from 0.5m to 3m.The axial force of lining structure is doubled and the bending moment is increased by two times.The stress of lining structure is aggravated,which is not conducive to long-term stability.(2)There are cavity defects behind the lining to change the stress state of the lining structure.With the increase of the cavity size,the lining structure near the cavity will be changed from small eccentricity to large eccentric coMPression,from coMPressive stress to tensile stress,and the tensile stress will increase with the increase of cavity size.The existence of tensile stress can easily cause cracks in concrete members,which is consistent with the existence of cracks behind the actual tunnel lining.(3)The existence of cavitys behind the lining affects the safety performance of the tunnel lining structure.The safety factor of tunnel lining structure decreases with the increase of the cavity size.When there is a large cavity behind the lining,the safety factor of the lining structure will be reduced to less than 1,and the lining may be damaged and lose the bearing capacity.(3)In this paper,the classification of the tunnel behind the tunnel lining is investigated,and the safety factor is determined as a grading index.Combined with the results of numerical theory,the degree of cavity defect behind the lining is divided.The circumferential width and radial depth range corresponding to the minor,serious,serious and serious hole defects under the condition of grade IV and grade V are determined,which provides a theoretical reference for the classification of the hole defects in the field.(4)In view of the causes of the cavity behind the tunnel lining and the possible damage characteristics,this paper puts forward two kinds of treatment countermeasures,i.e.backfilling grouting and lining reinforcement,and applies the proposed treatment measures to typical engineering cases to verify the effectiveness and feasibility of the scheme.