Research On Time-dependent Interface Damage Evolution Mechanism Of Ballastless Track In High-speed Railway

Ballastless track has become the main track structure of high-speed railway in China,and its longest service time has been more than 10 years.The construction and operation experience showed that the interface damage of ballastless track became an outstanding problem,which affected the safe service of track structure.The field investigation showed that the the engineering characterization and mechanism of interface damage were complex.Ballastless track might problem in the early age of the structure,and would gradually deteriorating and cracking under the temperature,train and other long-term cyclic load,its essence is the time – dependent damage in the whole life cycle.Most of the existing analysis methods mainly focus on the monotonic cracking processof ballastless track interlayer interface,the time-dependent interface damage evolution mechanism of ballastless track in high-speed railway is still unclear.And there is a lack of corresponding analysis methods to study the evolution law of time-dependent damage of interlayer.With the support from key projects of the National Natural Science Foundation of China(NSFC)and China State Railway Group Co.,Ltd,the paper constructed interlayer nonlinear analysis models for the different service characteristics of the interlayer interface in construction and operation phases respectively based on the time-dependent effect,and the interface of track slab-self-compacting concrete of CRTS ? slab track was taken as an example,the risk and evolution of interlayer damage of ballastless track during construction and operation phases were studied,and the influence mechanism of interlayer damage on the dynamic characteristics of ballastless track lines was also analyzed.The paper aims to develop a numerical simulation method to evaluate the risk assessment of interlayer damage of ballastless track during its construction and operation period.The main research work and results of the paper are as follows:(1)the study on the time-varying loading parameters of the ballastless track:Through investigations and testing,load parameters such as the cyclic temperature of the ballastless track during the construction period,exothermic hydration of selfcompacting concrete,shrinkage of self-compacting concrete,the long-term cyclic temperature of the ballastless track during the operation period,and long-term dynamic train load were studied.The incremental method was proposed to calculate the cumulative effect of the shrinkage stress field in the early age.Based on the time-frequency analysis method,the characteristics of the long-term temperature field were extracted and the longterm temperature load pattern of ballastless track was constructed.(2)the study on the time-dependent damage analysis model:For the slab-self-compacting concrete interface of CRTS ? slab track,the time –dependent damage analysis model was built according to its new and old concrete bonding surface performance.In the time – dependent damage analysis model,an early age analysis model of interlayer interface of ballastless track was established to solve the problem of interface damage analysis under the time-varying characteristics of materials and loads during the construction period.Based on the interaction pair,the bilinear cohesive behavior was restored,and a time variable was introduced through the secondary development of the FORTRAN self-programmed program to realize the coupling loading of the early-age multiple load fields and the embedding of the material time-varying parameters in the model.Aiming at the problem of predicting interlayer fatigue crack propagation of ballastless track under long-term load cycling,a constitutive relationship of fatigue cohesive behavior of ballastless track interface was proposed based on the stress-strength interference theory and performance degradation model.An independent strength and stiffness degradation model were used to describe the "gradual degradation"of the boding performance and the softening process of the cohesive model was used to control “sudden degradation" of the boding performance under long-term cyclic loading.A fatigue calculation program was also compiled so that the constitutive relation could be embedded in the model.(3)the mechanism of interlayer damage of CRTS III slab track during the construction period:Based on the early age analysis model,the risk and the evolution law of interlayer damage of slab-self-compacting concrete interface was revealed.The coupling effect mechanism of the early-age load fields on the interlayer damage was clarified,and the and the influence of key parameters such as bonding performance,shrinkage load,construction season and restraints of withholding device on the interlayer damage law was also studied.(4)the mechanism of interlayer damage of CRTS III slab track during the operation period:Based on the fatigue cohesive model,the interlyar the interface damage extension mechanism under long-term cyclic loads waa revealed,and the influence of early initial separation and bonding strength on the interlayer fatigue mechanical properties of ballastless track was also proved.Based on the subspace iteration method,the influence of interlayer separation on the modal of ballastless track was analyzed.A dynamic evaluation model of ballastless track was established by introducing structural static mechanics information.Based on restoring the bearing state of ballastless track foundation,the influence of interlayer separation on the dynamic performance of the structure was revealed.(5)suggestions for interlayer interface performance management of CRTS? slab track:The evaluation indexes of interface damage of ballastless track were summarized.Based on the time-dependent damage evolution law,suggestions for management of early-age interface performance were put forward from the aspects of volume stability of self-compacting concrete,interlayer bonding performance,construction method,etc.Based on the law of interface fatigue damage propagation in operation period,the strength of interlayer bond was suggested.The evaluation index of separation in operation period was suggested according to the dynamic influence mechanism.