Study On Effects Of Maintenance And Repair Measures On Mechanical Behaviors Of The CRTSⅡ Slab Track

CRTSⅡ slab track is one of the main ballastless track types in China.After more than 10 years of service,CRTSⅡ slab track has suffered from such defects as the gap between the track slab and CA mortar layer,the arching at slab end and the damage of the wide and narrow joints.The longitudinal continuous characteristics of the track and high temperature load are the main reasons for the above diseases.Accordingly,at present,there are mainly two kinds of track maintenance ideas: one is to strengthen the load bearing capacity of the track structure by strengthening the connection between the structural layers,such as the maintenance measures of post installed rebars between the track slab and the concrete base,and glue injection between the track slab and the CA mortar layer;The second is to reduce the rail temperature load,such as reflective thermal insulation coatings.The maintenance measures have changed the original load transfer path or stress characteristics of the ballastless track,making the track structure form a new mechanical balance system.Knowing the deformation,stress,damage and other mechanical behaviors of the new system under high temperature load is the basis for maintaining the track service state and ensuring the safe operation of ballastless track.However,the mechanical behavior of CRTSⅡ slab track after maintenance measures are taken needs to be further studied.In this thesis,the deformation,stress,damage and other mechanical behaviors of CRTSⅡ slab track under high temperature load before and after the use of maintenance measures are compared.The influencing factors and laws of different maintenance measures on track mechanical behavior are analyzed.Optimization suggestions that provide guidance and reference for damage control of ballastless track are put forward.The specific research contents are as follows:(1)The mechanical behavior analysis model and method of CRTSⅡ slab track after maintenance are proposed.The bond performance of the post installed bars in the concrete base and track slab is studied by means of experiments,and the corresponding mathematical models of the bond slip nonlinear constitutive relationship of the installed bars are established respectively.Based on the experimental results,a simulation method for the anchorage of the post installed bars is proposed,and the influence of the hole state of the post installed bars on the bond performance of the post installed bars is studied;Based on the cohesion theory,a method to characterize the nonlinear constitutive relationship of interfacial bond slip before and after glue injection is proposed;Based on the temperature distribution theory of concrete slab,the vertical temperature distribution law of track slab before and after the application of coating is studied,and a nonlinear characterization method of temperature distribution of track slab is proposed;Combined with the plastic damage theory of concrete,a finite element model for mechanical behavior analysis of ballastless track after maintenance is established,which fully considers the nonlinear interaction between components,the nonlinear temperature load of track and the nonlinear constitutive relationship of materials.The correctness of the model and the necessity of considering the nonlinear characteristics are verified by comparing with the test results.(2)The influence of maintenance measures on the mechanical behavior of CRTSⅡ slab btrack is studied.Based on the mechanical behavior analysis model of CRTSⅡ slab track after maintenance,the mechanical behavior of ballastless track under high temperature load before and after maintenance measures are compared and analyzed for the three maintenance measures of post-installed rebars,glue injection and coatings;The influence of relevant factors of maintenance measures(number and state of postinstalled rebars,size and performance of glue injection interface,thermal insulation performance of coatings,etc.)on the mechanical behavior of ballastless track after maintenance under high temperature load is studied,and the influence of existing service state of track(original interlayer interface state,wide and narrow joint state)on the mechanical behavior of ballastless track after maintenance is analyzed.The results show that when the holes are wet or dirty,the elastic stiffness and ultimate bond strength between the concrete and the rebar decrease by 11%-37%,and the maximum vertical displacement at the end of the track slab increases by 4%-7%,compared with the clean situation of the holes for post-installed rebars.The holes should be kept clean during construction.The effects of glue injection measures on preventing track diseases are closely related to the size of glue injection interface.When the total depth of glue injection is greater than 47% of the width of track slab,the possibility of interface gapping for the ballastless track after glue injection under the high temperature load is significantly reduced;When the nonlinearity of the temperature distribution of the track slab NU is 0.17,the arch displacement and the ratio of interlayer debonding is about61% and 168% respectively when NU is 0(the nonlinearity of the temperature distribution is ignored).The influence of the nonlinear characteristics of the temperature distribution of the ballastless track should be fully considered in the evaluation of the cooling effects of coatings.(3)The analysis and evaluation method of mechanical behavior of CRTSⅡ slab ballastless track under the condition of multiple measures sharing is proposed.Based on the mechanical behavior analysis model of CRTSⅡ slab track after maintenance,the deformation characteristics and damage distribution characteristics of ballastless track structure under different measures are analyzed;The ability of single measure,double measures and three measures to prevent the damage of ballastless track structure is compared.The results show that for the conditions with initial damage of concrete joints and initial debonding between layers,when the two maintenance measures are used together,the effect of combined use of post-installed rebars with any other measures is better than that of coatings and glue injection in restraining the arching and interlayer damage at the end of track slab;The vertical displacement of the end of the track slab can be reduced to less than 20% when post-installed rebars and used with another measure.