| The CRTS? slab track is one of the slab track structures with the largest mileage in China,which has been used for more than 10 years and has a good performance.However,the interface crack between slab and mortar layer has been observed in CRTS? slab track under the influence of complex external environment,which reduced the smooth of track and the safety of running operation.Therefore,it is necessary to study the mechanism and improvement methods of interface crack of slab track.The crack of slab track is a fracture of mixed mode experienced a complex loading-unloading-reloading process.The reasonable simulation of the interaction between the layers of slab track is the key to study the interface crack.But the existing models of interface disease of slab track have some problems,such as the stress oscillation of crack tip and self-repairing,which could not simulate mixed mode of interface crack accurately.Besides,the influence of construction and operation conditions on the interface crack of slab track has not been considered comprehensively in the existing study of disease mechanism.There are still some problems in the treatment of interface diseases so far,such as the recurrence after restoration,the secondary damage from treatment.Therefore,it is necessary to study the mechanism and improvement methods of interface crack of slab track on the basis of improving the analysis method of interface disease.This paper was aimed at the research on the interface disease of slab track in high-speed railway,and mainly supported from the projects of National Natural Science Foundation and the China Railway Corporation.The mechanism and influence factor of interface crack in slab track during the process of construction and operation were investigated based on the analysis models and methods of interface crack in slab track.The treatment of typical interface diseases was proposed.The main contents and conclusions are summarized as follows:(1)The multi-layer characteristics of CRTS ? slab track system were summarized,and the parameters of slab track and load were selected based on experiment and literature.The multi-layer characteristic of slab track was analyzed from the aspects of structure design,material difference and construction order,etc.And it is pointed out that the CRTS? slab track is a multilayer composite structure with multiple young and old concrete bonding interface.The interface was a weak link and need to be focused.Besides,the parameters selection of CRTS? slab track,the temperature load,the dynamic load of train,and the foundation deformation was investigated based on the literature as well as the full-scale slab track experiment.(2)Establishment of nonlinear finite element analysis model and method for interface cracking of CRTS II slab trackAiming at the disadvantages of mixed mode fracture simulation in existing interlayer cracking models,an improved cohesion model was proposed,and the interface mix-mode cracking analysis module based on an improved cohesive model was developed.By coupling the analysis module IMCAM with the slab track FEM model,a nonlinear finite element analysis model for interface cracking of CRTS? slab track was established,which could accurately simulate the interfacial mixed mode fracture.By comparing this model with the existing simulation methods and test results,the improved constitutive relation of cohesion and finite element model were verified.(3)Research on the mechanism and control method of interface cracking between slab-mortar layer under daily temperature variation and tension operation during constructionBased on the nonlinear finite element analysis model for interface cracking of CRTS? slab track,the formation and development law of interfacial stress and damage between slab and mortar layer under diurnal temperature variation and tension operation were studied.The results showed that the temperature change had significant influence on the interfacial stress and damage of the mortar layer,and much attention should be paid to the temperature change after grouting CA mortar.The evening of the day was a good time for CA mortar grouting,and it was suggested that the temperature change of track after construction should be controlled.Increasing the interfacial bond strength could effectively increase the cracking temperature,and it was also suggested that the bonding strength of mortar layer at 1day after construction should been improved.Under the influence of diurnal temperature variation in spring,summer and autumn,the interfacial stress of mortar layer is relatively large.In addition,the temperature of CA mortar grouting construction should be also strictly controlled.Besides,tension operation would improve interfacial stress of slab-mortar interlayer,and it was suggested that the temperature of tension operation should be controlled within 5?.(4)Study on mechanism of interface cracking of slab-mortar under complex operating conditions such as temperature,vehicle load and bridge pier subsidence.Taking full consideration of the effects of temperature,vehicle load and bridge pier subsidence,the cracking mechanism of slab-mortar interface under operating conditions was studied based on the nonlinear finite element analysis model for interface cracking of CRTS? slab track.The research result showed that under the action of daily temperature variation,the interface appeared brittle cracking.When the dynamic vehicle load was loaded,the crack expands further.Besides,the differential settlement of bridge piers would lead to a wide range of mortar interface crack,which should be strictly controlled.The uneven constraint on the slab of wide-narrow juncture defect would make it be partial pressure,which could lead to an end buckle of the slab.The defect of narrow juncture had the most signification on the buckle displacement.When the defect height of narrow juncture reaches 40mm,maintenance plan should be arranged as soon as possible.(5)Study on the repair material parameters for slab-mortar interface gap,the reinforcement implantation for slab buckling prevention&control,and the anchoring scheme for slab buckling maintenance.Based on the interface cracking model,the repair&treatment measures of slab-mortar layer interface gap and slab buckling deformation were studied.The study showed that increasing the bond strength of the interface repair material could increase critical cracking temperature.At the same time,increasing the elongation at break of repair material could obviously improve remediation effect of interface cracking.It was recommended that the bond strength of the repair material should be not less than 3 MPa and the breaking elongation should not less than 30%.As for prevention and control of slab buckling deformation,reinforcement implantation at both end of slab could effectively limit the slab buckling deformation,it was suggested that it should plant 2 bars at both end of slab.The interface shear resistance for different rebar planting schemes was compared,and the anchoring scheme and applicable conditions of the planting reinforcement of buckling slab were proposed in the paper. |
PDF Full Text Request