The Influence Of Poor Contact State Between Tunnel Lining And Surrounding Rock On The Safety Of Lining Structure

Poor contact between tunnel lining and surrounding rock was an important factor for lining structure cracking and other diseases,which will threaten the safety of lining structure seriously.In this paper,the influence of different contact states between tunnel lining and surrounding rock on the safety of lining structure was studied.Through means of theoretical analysis,modelling test,numerical simulation and engineering application,the detection method,influence laws and safety evaluation of contact states between lining and surrounding rock were researched.Firstly,based on the literature research,the genetic characteristics of the poor contact between tunnel lining and surrounding rock were analyzed.Forward calculation was conducted and verified by the physical simulation test.The characteristics of apparent resistivity anomalies curve of transient electromagnetic method(TEM)under the condition of poor contact between tunnel lining and surrounding rock were summarized.Secondly,the numerical simulation was used to study the influence of cavities and loose contact state behind lining on the safety of lining structure.Considering the variation of the distribution of the pressure of surrounding rock along the direction of the tunnel,the load-structure model in the condition of cavities behind lining was modified.Thirdly,based on the influence characteristics of the poor contact state behind lining structure,a comprehensive evaluation system on the safety of lining structure was established.Finally,the research results were applied on an operational tunnel,and the actual effects of the results were verified.The main research results were as follows:(1)Through forward calculation and physical simulation of three layers of media in different contact states behind lining,the feasibility of detection of contact states behind lining by using transient electromagnetic radar(TER)was explored.Four types of electric sounding curves corresponding to different contact states between lining and surrounding rock were obtained.(2)The three-dimensional(3D)mechanical response of the lining structure under the condition of cavities behind lining was studied,the variation laws of internal force and contact pressure of lining structure with the area of cavity were analyzed,the characteristics of influence of the cavity on the main stress direction of lining,normal and tangential contact force between lining and surrounding rock were clarified.The effect of the position and area of the cavity on the mechanical behavior of the lining structure were studied.Finally,the load-structure model under the condition of cavities behind lining was modified.(3)The impact of loose contact states between tunnel lining and surrounding rock on the safety of lining structure was analyzed.The relationship of the proportion of the insufficient strength of the back-fill grouting,and the percentage of the compactness in the loose contact area behind lining structure with the internal force,the stress,the contact pressure,and the deformation of the lining structure were studied.The influence law of loose contact area on the safety of lining structure was explored.Finally,the safety influence level of the lining was divided.(4)Based on the AHP-entropy method,which the subjective and objective weight was combined in the evaluation model,and considering the characteristics of the poor contact state behind lining on the safety of lining structure,a comprehensive evaluation system used for assessing the influence of poor contact state behind lining on the safety of lining structure was established.Based on the lining quality evaluation in a railway tunnel,the application effects of TER and ground penetrating radar(GPR)in the detection of lining thickness and contact states behind lining were verified.The internal force and stress variation law of the lining structure were compared and analyzed under the condition of multiple cavities behind lining.According to the comprehensive evaluation results of the influence of poor contact state behind lining on the safety of lining structure,the corresponding treatment measures were proposed.The research results can provide references for similar projects at home and abroad.