Effect Of Tunnel Lining Cavity Behind Operation And The Countermeasures

With the growing number of tunnels being into operations in china,the tunneldiseases have attracted more and more concern. Therefore, select the Tunnel cavitywhich makes a significant impact on the tunnel as the research object.The cavities with different shapes and different sizes which exist behind thesecondary lining of operational tunnel vault make an important effect on the structure.The effect is researched by numerical simulation based on the Xiaoyakou tunnel in thispaper. And analysis the safety factor under different working conditions by calculatingthe ultimate tensile strength of concrete. Then present the relevant disposal measures fordifferent cavities.This article will simplify the cavity on the tunnel vault as rectangles and trianglesin cross section. The changing of three aspects is mainly studied in this paper：verticalheight changing, hoop width changing, longitudinal length changing. Get thedisplacement and stress conditions of the tunnel surrounding rock mass and thechanging conditions of tensile stress and compression stresses of the secondary liningundercavities by the analysis of the three different conditions. Surrounding rock stresswill become more complex when cavities exist behind the secondary lining. In order toprovide a comprehensive analysis of the cavities’ impact on the overall stability of thetunnel structure, the ultimate tensile strength of concrete is applied to get the safetyfactor of tunnel.In order to analysis the effect cavitiesmake on the surrounding rock during theoperation of the tunnel,the force and deformation characteristics ofsurrounding rock andsupporting structure under different cavity conditions is researched based on the project.The result indicates that, first when the tunnel is constructed under Ⅴ gradesurrounding rock, the cavities behind the secondary lining do not much effect thedisplacement of the whole structure and the compressive stress of surrounding rock nearthe cavities. Then, when each size of cavitiesdecreases, stress of secondary liningbehind cavities shows different degree decreasing. And the changing of ring size ofcavities makes the most impact on the supporting structure of lining. Also get that, thetunnel structure stress changes when the ring size of cavities reaches1/7of the tunnelcontour.Finally sum up the cavity effect on the safety of tunnel structure is roughly as follows:the cavities size of different direction influence on structure safety factor, frommost significant to least significant: ring width, longitudinal length, vertical height.Among them, when the ring size of cavities reaches1/7of the tunnel contour,thereducing of tunnel structure safety factor becomes remarkable.