| With the large-scale development of domestic rail transit construction projects,the problem of tunnel lining structure disease also emerged,and subway tunnel lining disease caused serious safety hazards to tunnel traffic.The tunnel lining crack is the most common lining disease,and most of the tunnel linings in operation are working with cracks,so it is important to study the crack evolution mechanism of underpass tunnel lining structure and the safety of lining structure.This paper takes the tunnel crack disease detection projects from Shigao Station to Miaoling Road Station interval of Qingdao Metro Line 2,Metro Building to Haier Road interval of Line 3 and Wusi Square to Wubuling interval as the background,takes tunnel lining cracks as the research object,adopts the particle discrete element method,establishes the discrete element model of surrounding rock and metro tunnel,studies the development and expansion law of lining cracks,and finds out the tunnel lining crack evolution law and weak position according to the simulation results,as the basis for establishing the evaluation system,proposes the safety state grading evaluation system with cracked lining,and achieves the main conclusions and results as follows.(1)Through the on-site inspection of the disease in typical sections of Qingdao subway tunnels,the distribution pattern and geometric shape characteristics of the lining disease were summarized to provide a reference basis for the next numerical simulation.In terms of the orientation of lining cracks,47% of the cracks are circumferential cracks,32% of the longitudinal cracks,14% of the oblique cracks and only 7% of the reticulated cracks.According to the distribution location of lining cracks,62% of cracks are in the arch waist,followed by 27% in the arch top,and 11% in the arch shoulder.In terms of crack geometry,the crack length distribution interval is concentrated in 3～9m,the crack depth is mainly concentrated in 60～120mm interval,and the crack width is mainly distributed between 0.2～0.8mm.The overall condition of the crack disease is good,and the form of cracks is most in the form of circular cracks,which are mostly tiny cracks with low degree of crack development.(2)The modeling of the surrounding rock and lining was completed by using the particle flow code and the calibration of the fine-scale parameters,and the specimen models of the surrounding rock and lining materials were established.The corresponding macroscopic parameters of the surrounding rock and lining materials were determined by uniaxial experiments and shear tests,and the appropriate fine parameters of the discrete element model particle and contact models were calibrated.The characteristics of different model intrinsic relations are compared,the parallel bond model is selected to define the contact between the particles,the method of deleting the connection is selected to simulate the tunnel lining cracks,and the modeling of tunnel lining of tunnel with cracks by particle flow method is completed.(3)The discrete element particle flow method was used to analyze the distribution and expansion law of the lining crack state under the condition of lining crack existence,and the displacement distance of the loading wall unit when the preset crack completely penetrates the lining was used as a side indicator to reflect the crack hazard degree.The displacement of the loaded wall unit is the largest when the preset crack completely penetrates the lining at the arch waist position,followed by the preset crack at the arch shoulder position,and the displacement of the loaded wall unit is much smaller when the preset crack completely penetrates the lining at the top of the arch than at the arch shoulder and arch waist,and the displacement of the loaded wall unit decreases linearly with the increase of the depth of the preset crack,and the change of the preset depth has a more significant effect on the arch shoulder of the lining structure.When multiple cracks are preset,there is a tendency for the cracks to connect with each other,and there is a risk of spalling off blocks at the preset cracks,and the more the number of preset cracks,the greater the impact on the safety of the lining structure.When the cracks are preset on the top and shoulder of the arch,the expansion and development of the cracks are mainly affected by tensile stress,when the cracks are preset on the waist of the arch,the expansion and development of the cracks are affected by tensile and shear stress,the tensile cracks mostly penetrate the lining,the shear stress is unfavorable to the crack resistance of the lining section,the shear cracks generally appear along the direction of the axis of the flat section of the lining,which leads to the tendency of spalling of the tunnel lining.Cracks develop along the weak parts of the lining section,when the preset cracks exist,the cracks first start to expand along the preset cracks,and then cracks appear at other locations,when the preset cracks are in the vault,the lining cracks cracking and development order is: vault → arch spandrel → arch foot,when the pre-set cracks arch spandrel,arch spandrel inside → vault → arch spandrel outside → back arch,when the pre-set cracks arch lumbar,arch lumbar inside → arch foot → arch spandrel.(4)A tunnel lining tunnel cracked lining safety state evaluation model was established,and the feasibility and reliability of the grading method was verified by combining with the actual Qingdao underpass tunnel inspection project.The safety state evaluation model of tunnel lining cracks was constructed,and the lining crack geometry,crack density condition and crack distribution condition were selected as the primary indicators,and the length,width,depth and crack orientation,parts and number of cracks were taken as the basic indicators,based on the field inspection data and numerical simulation results,the subordinate degree function of each indicator was refined,and the evaluation table of tunnel lining disease state was determined The safety status rating of lining cracks was carried out by calculating the final fuzzy judgment matrix. |
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