| The 19th National Congress of the Communist Party of China put forward the critical goal of developing China into a transportation power in the middle of the 21st century.The transportation field is still the top priority of national economic and social development in the next few decades.Highway tunnels have become one of the most critical highway transportation infrastructures because of their unique advantages.Due to the limitations of construction technology and operation and maintenance conditions,highway tunnels generally have different degrees of diseases during the operation period,and the cavity behind the lining is a common internal defect.The hole behind the lining changes the "contact state" between the lining and the surrounding rock,causing the redistribution of the surrounding rock pressure acting on the lining structure,causing the surrounding rock load and stress concentration near the cavity,worsening the stress state of the lining structure,thereby accelerating the lining deterioration process,and bringing great hidden dangers to the safety of the tunnel structure.In this paper,the lining structure of a highway tunnel under the condition of the cavity behind is taken as the research object,combined with the tunnel inspection items and inspection requirements during the operation period,the multi-parameter automatic identification method of the cavity behind the lining is studied using field test,theoretical derivation,indoor model test,and numerical simulation,and the calculation method of the lining surrounding rock pressure is established to quantitatively analyze the bearing capacity of the structure under different cavity and lining crack conditions,Based on the transitive reliability model,a quantitative evaluation method of phased lining stability is established to realize the quantitative evaluation of lining strength under the condition of the cavity behind.The main research results are as follows:(1)Based on gprmax radar signal forward simulation,the propagation law and reflection characteristics of gprmax radar signal under different cavity conditions are obtained,and the gprmax gprmax radar detection model test device behind the lining is developed.According to the model test results,the characteristics of GPR hole signals in the time domain,frequency domain,and time-frequency domain are revealed,and the differences in characteristic parameters such as standard deviation,amplitude,spectral entropy,and imf1 component between hole-free signals and hole signals are analyzed.Based on the S VM binary classification algorithm,a multi-parameter automatic recognition method for GPR cavity signal is established,and a multi-parameter automatic recognition program behind highway tunnel lining is developed using MATLAB software.The multi-parameter automatic identification method of the cavity behind the tunnel lining has an identification error of 12.5%for the cavity model test signal and 18.3%for the tunnel field cavity signal.The accuracy of hole identification is improved by multi-parameter automatic identification,which effectively solves the problem that hole signal identification depends on manual experience and low efficiency.(2)The cavity behind the lining changes the pressure distribution state of the surrounding rock of the lining.Based on the ABAQUS simulation,the pressure distribution law of the surrounding rock of the lining under the condition of the cavity behind the lining is obtained,and the pressure mechanics model of the surrounding rock of the lining under the condition of the cavity behind the lining is established.Considering the location,circumferential span,and surrounding rock parameters of the back cavity,based on the calculation principle of the load structure method,the theoretical calculation method of the lining surrounding rock pressure under the condition of the back cavity is deduced and established,and the theoretical calculation formulas of surrounding rock pressure of the back cavity with symmetrical distribution and asymmetric distribution and concentrated load near the cavity are given respectively.The errors between the theoretical calculation results and the numerical simulation results are 8.9%and 8.1%,respectively.The accuracy of the calculation method is verified.Based on the calculation formula of the lining surrounding rock pressure under the condition of the cavity behind,the parameter analysis of the influence of tunnel covering rock parameters and cavity parameters on surrounding rock pressure is carried out,and the variation law of concentrated load of the lining surrounding rock near the cavity with surrounding rock and cavity behind parameters is revealed.(3)Based on the basic principle of model mechanical test of highway tunnel lining,a horizontal model test platform of tunnel lining was developed,and the model test of lining crack law under the condition of the back cavity was carried out,which revealed the crack law and instability mode of lining structure under the condition of back cavity.It is found that the deformation and instability of lining can be divided into three stages:Ⅰ.elastic deformation of lining model,Ⅱ.Local crack plastic deformation of lining model,and Ⅲ.instability and large deformation of the lining model.The cavity behind the arch crown changes the stress and deformation distribution of the lining,resulting in the early occurrence of structural cracking at the arch crown of the lining;The cavity behind the spandrel and the spandrel causes asymmetric stress and deformation of the lining.The lining cracks not only exist near the cavity but also on the side without the cavity.The ABAQUS connector element is used to establish the mechanical calculation model of the lining surrounding the rock,and the simulation analysis of the bearing capacity of the lining under the condition of the cavity behind is carried out.According to the distribution of lining bending moment and axial force,the various rules of safety factors of different sections of lining arch under different cavity conditions are obtained.Through the lining model test and numerical simulation,the instability mode and bearing capacity change law of lining structure under the condition of the cavity behind is revealed.(4)Based on the crack characteristics of highway tunnel lining,the influence of cracks on the bearing capacity of lining under different lengths,strikes,and depth is systematically studied,and the calculation formula of a single characteristic parameter and bearing coefficient of cracks is established.According to the influence law of different crack parameters on bearing performance,combined with the common combined crack forms in tunnel lining structure,the crack length coefficient Cl and strike coefficient C are established by step fitting cp And depth coefficient ch.The influence factors of the combined crack bearing coefficient are clarified,and the calculation method of combined crack bearing performance is modified combined with fractal theory.The quantitative correlation between lining crack damage characteristics and bearing performance is established,and the quantitative analysis of the lining "crack damage process" under the condition of the cavity behind is realized.(5)According to the inspection items and requirements of tunnel highway tunnel during the operation period,the lining stability evaluation index system under the condition of the cavity behind is constructed to objectively and quantitatively describe the status of each evaluation index so that the evaluation of various qualitative or quantitative indexes with different physical meanings,different units,and different states has the same goal.Based on the hierarchy and logical relationship of lining stability evaluation indexes,comprehensively considering the characteristics of cavities,cracks,and deformation behind the lining,combined with the transitive reliability model,the quantitative evaluation method and application process of lining stability in stages are established:cavity identification→load calculation→bearing analysis→stability evaluation,which effectively overcomes the problem of insufficient quantification of traditional evaluation methods.Taking Jinan Kaiyuan tunnel as the engineering background,the engineering application of the lining stability evaluation method is carried out,and the quantitative evaluation of the stability of the lining section with a cavity behind it is carried out. |
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