Study On Classification Of Safety State Of Lining Cracks In Beijing Metro Section And Crack Treatment Method

With the large-scale expansion of the domestic rail transit construction project,the problem of tunnel structure diseases has emerged.The disease of the lining structure of the subway and the safety hazard of operating the tunnel are a problem that cannot be ignored.At present,there are few studies on the safety status of the lining structure of subway tunnels in China.In particular,the research on the classification of the safety status of subway lining structures needs to be continuously deepened and improved.Based on the field investigation of tunnel diseases in Beijing Metro,this paper studies the distribution and expansion of the disease of subway lining;according to the results of statistical analysis,the tunnel three-dimensional loading device is designed and used.The loading model was carried out on the fracture model,and the evaluation system of the safety state of the lining structure was established.The crack treatment methods are discussed from the aspects of preventing and restraining crack propagation in the early stage and repairing and reinforcing cracks in the later stage.The main research results obtained are as follows:(1)Through the investigation of the disease of six typical lines with frequent diseases in Beijing,the results show that the form of the disease of the subway is mainly lining cracking,followed by water seepage and leakage,tunnel voiding,frost boiling and mud pumping of the track bed,and cracking and misalignment of the segments.Four representative intervals were selected for special statistics.The distribution of cracks in the lining structure of each interval and the geometric characteristics of the cracks were analyzed to provide a basis for the determination of the experimental conditions.Comparing the intervals,it is found that with the accumulation of the operation period of the subway tunnel,the degree of cracking of the lining structure and the dispersion of the crack width are increasing.(2)A model experiment with a similarity ratio of 1:10 was designed,and the loading platform of the three-dimensional model was worked out according to the actual engineering parameters,and the corresponding similar materials of the tunnel lining were allocated.Finally,a set of loading experiment method of model method was formed.Based on the results of statistical analysis of lining diseases,a total of five sets of experiments were selected,namely:a complete lining structure,a prefabricated crack structure of different strikes,and a prefabricated crack structure of different parts,the structure of two prefabricated cracks at different intersection angles,the structure of two prefabricated cracks combined in different parts,a total of 14 common crack patterns in the experimental loading of the model.(3)Based on the results of the loading experiment,the vertical and horizontal deformation laws of the intact tunnel structure are revealed.The crack distribution and expansion law of the lining structure are obtained.For a prefabricated crack tunnel,the influence of the direction of the crack on the bearing capacity of the structure from large to small is:longitudinal,inclined,and circumferential;the influence of the location of the prefabricated crack on the bearing capacity of the structure The order of degree from big to small is:vault,arch foot,arch lumbar and spandrel.The size of the geometry of the crack has the greatest influence on the bearing capacity of the tunnel structure,followed by the direction of the crack and the location of the crack.(4)For two prefabricated tunnels,the effect of the two cracks on the bearing capacity of the tunnel is greater than that of one prefabricated crack.However,the loss value of its bearing capacity is not the sum of the loss values of the bearing capacity of the corresponding two prefabricated crack structures.The combination of the different positions of the two prefabricated cracks has an effect on the ultimate load carrying capacity greater than the effect of the intersection angle of the two prefabricated cracks.(5)Based on the model loading experiment,the deformation law of the tunnel structure,the force and damage characteristics of the structure are obtained,and the safety evaluation system of the lining structure is constructed.Based on the theory of fuzzy mathematics,the method of analytic hierarchy process is used to calculate the reduction factor of the bearing capacity of the damaged structure,determine the damage level of the structure of the fracture,and finally achieve the purpose of classification of safety evaluation.This grading method is used to assess the level of damage to a section of the subway in Beijing.(6)Using the numerical calculation method,the force of the lining and steel bars of the cracked and intact structure during the loading process is studied,and the influence of the cracking condition on the bearing capacity of the lining is obtained.The structure of the crack is treated by the local repair method and the overall reinforcement method,and the influence of different reinforcement methods on the bearing capacity and crack resistance of the structure is obtained.