Study On The Tunnel Structure Safety Under The Impact Of The Lining Thickness Deficiency

With the acceleration of transportation,the scale of tunnel construction is also increasing.However,most of old Chinese highway tunnels have showed severe deterioration and reduced performance at present,seriously affecting the traffic quality and personal safety.Lining thickness deficiencies is the most important reasons for lining cracking,leakage of water and other tunnel defects.Therefore,based on a two-lane highway tunnels,the experimental investigation and the numericial simulation were conducted to examine the effect of lining thickness deficiencies on the progressive failure process of tunnel linings.The earth pressure between the surrounding soils and the tunnel linings,the stress,deformation and failure of the tunnel linings were also analysed.A Bayesian Networks model was developed for the forecasting of the tunnel structural safety.The main contents and results are as followes(1)By carrying out the model test,the influence of insufficient lining thickness at different locations on the safety of tunnel structure was studied.The results show that the lining has tensile cracks on the inner side of the inner arch,the inner side of the arch and the outer side of the side walls,and the crushing phenomenon appears on the inner side of the side wall;when there is insufficient thickness defect in the lining arch,the lining defect and the surrounding rock The contact pressure is reduced,and the contact pressure of the adjacent position is increased;the structural internal force(the axial force and the bending moment)at the lining defect is reduced,the structural deformation is obvious,the cracking condition is serious,and the tunnel bearing capacity is reduced.The model test results are verified by numerical simulation.The results show that the numerical simulation results are in good agreement with the model test results.Compared with the lining without defects,the insufficient thickness of the lining causes the local stiffness of the structure to be significantly reduced,which seriously affects the mechanical characteristics and the failure law of the structure.When the lining thickness deficiency of the arch,the rigidity of the defect position is reduced,resulting in a decrease in the local bearing capacity of the structure,the settlement of the dome is obvious,the contact pressure at the defect position is significantly reduced,and the contact pressure at the adjacent position is increased;When the thickness is insufficient,the horizontal convergence is conspicuous,the contact pressure at the defect position increases,and the contact pressure change at the adjacent position is small.The internal force of the defect position(axial force N and bending moment M)reduces the crack propagation speed,and finally the crack area increases,and the cracking situation is serious.(2)Through the numerical simulation of the experimental scheme of the thickness of the test lining with different thickness and extent at the vault,it is found that with the increase of the depth and range of the thinning,the contact pressure between the dome and the surrounding rock is reduced,and the internal force of the structure is reduced.(Axial force and bending moment)decrease,the number of cracks increases,the final depth of crack increases and the final area of typical crack increases,the structural load capacity decreases,and the lining cracking is more serious.It shows that the thickness and range of thinning have a great influence on the safety of the tunnel structure.(3)Based on the theories and methods of Bayesian Networks,the location,extent and thickness of the lining defects are taken as the main risk factors.The test results of the vault settlement,horizontal deformation,crack depth,crack area and number of cracks in the numerical simulation results are taken as risks indicator.The safety risk analysis model of the tunnel lining structure when the lining thickness is insufficient is established,and the importance of the risk factors of the lining structure safety is analyzed.Based on the analysis results,this chapter establishes the safety risk control system of tunnel lining structure when the thickness of the lining is insufficient to provide the guarantee for the safety of the tunnel lining structure.