Research On Stability Of Highway Tunnel Cracks Based On Fracture Mechanics

According to the statistical analysis of the regular inspection of 21 highway tunnels in Youyang area,it is shown that the tunnel lining diseases account for the highest degree of maintenance concern of the tunnel diseases,and the longitudinal cracks account for the largest proportion of the tunnel lining diseases.In this paper,based on the theory of fracture mechanics and concrete fracture mechanics and the engineering test of composite fracture,the calculation formula of stability coefficient of different fracture types of tunnel is determined.The finite element software ANSYS is used for numerical simulation to calculate the stress intensity factor at the crack tip,and the change of stress intensity factor at different positions,depths and angles of the tunnel crack is studied,and the law of the instability propagation depth and stability factor change is analyzed through calculation.The research results can provide analysis and reference for the field monitoring data of tunnel lining cracks.The main research contents and achievements are as follows:1.Through the detection of tunnel diseases in Youyang area,the proportion of the number of tunnel diseases is statistically analyzed.According to the grading weight of various tunnel diseases in the specification,the maintenance attention coefficient of the tunnel is introduced to calculate and analyze the maintenance attention coefficient of the tunnel diseases,so as to provide the pertinence for maintenance and treatment.Based on the statistical analysis of the types of cracks in this area,it is found that the majority of longitudinal cracks in the tunnel are harmful to the lining structure,and when the width of the cracks is within 5mm,the depth,angle and position of the cracks are the important factors affecting the stability of the cracks.2.The finite element model of tunnel lining cracking structure is simplified by using ANSYS software.The stress intensity factors of single crack at the arch crown,arch waist and side wall,with different crack depth and angle are calculated by displacement extrapolation method.The change rule of stress intensity factors with crack depth and angle at each position is analyzed.The stress intensity factors under the double cracks of the arch crown and the arch waist,the arch waist and the side wall are calculated.3.Based on the analysis of fracture mechanics on different types of cracks in tunnel,the corresponding calculation formula of stability coefficient is established.The value of stress intensity factor calculated by finite element software is substituted into the formula,and the stability coefficient of cracks in different positions,depths and angles is calculated.By using the linear fitting of Origin software,the function relationship between the stability coefficient and the depth of the crack is fitted,and the unstable propagation depth of the crack at different positions and angles is obtained,and the instability propagation of the tunnel crack is analyzed.4.Based on the analysis of the stability coefficient of different crack angle and depth,the change rule of the stability coefficient with the crack depth,angle and position is studied.This paper analyzes the stability coefficient of the tunnel under the double cracks of the arch crown and the arch waist,the arch waist and the side wall,and studies the change rule of the stability coefficient under the combination of the single cracks and the double cracks.