Experimental And Numerical Investigations For Macro-and Meso-Mechanical Properties Of Glued Ballast Bed In High-speed Railway

Glued ballast bed is a new track structure formed by using ballast glue spraying technology,which makes ballast aggragates bonded.Compared with the traditional ballasted and ballastless track,glued ballast bed which has the characteristics of good integrity and high stability has been applied in railway around the world.Glued ballast bed of high-speed railway in China is mainly used to solve the problem of ballast-ballastless transition section and prevent ballast flight.However,the theoretical research of glued ballast bed lags behind the engineering practice,which leads to some blindness in engineering application,thus seriously restricts its further popularization and application.Therefore,the basic mechanical parameters,actual service performance and meso-mechanical behavior of glued ballast bed are inveatigated by combining indoor test,field test,theoretical analysis and numerical simulation,so as to provide theoretical support for the further application of glued ballast bed.(1)For basic physical and mechanical performance parameters of glued ballast bed,a series of laboratory tests were carried out,and the basic mechanical property parameters are determined.In terms of basic physical and mechanical performance parameters of glued ballast bed,including compression,tension and shear,the confining pressure loading test,uniaxial compression test,splitting tensile test and direct shear test were carried out through some selfdesigned equipment.The changes of compressive,tensile and shear performance parameters of granular ballast before and after bonding and under different glue dosages were compared and analyzed.The indoor test results show that the glued ballast specimens not only have improved compressive and shear properties,but also show tensile characteristics;the elastic modulus,compressive strength and tensile strength of glued ballast specimens show linear growth with the increase of glue dosage.With the increase of glue dosage,the cohesive force of the glued ballast increases linearly,while the internal friction angle decreases linearly.(2)The field test was carried out for the glued ballast bed of high-speed railway in service.The static structural parameters are obtained,and the vibration characteristics of different parts of track structure are revealed.For the field service performance of glued ballast bed,static and dynamic performance tests were carried out in the ballast-ballastless transition section of high-speed railway,and the changes of structural parameters such as lateral resistance,longitudinal resistance and supporting stiffness of glued ballast bed under different bonding modes were compared,and the influence of ballast glue on the vibration performance of different parts of track structure was also investigated.The field test shows that,compared with the common ballast bed,the lateral resistance,longitudinal resistance and supporting stiffness of glued ballast bed are increased gradually.For the vibration performance of track structure,the vertical vibration acceleration of rail,different positions of track bed and subgrade surface in track structure shows a strengthening trend after bonding,while the vertical vibration of sleeper shows a weakening trend.The predominant frequency of rail is more than 2 times higher than that before bonding,and predominant frequency of sleeper is obviously reduced.At different positions of the ballast bed,predominant frequency of vibration is increased compared with that before bonding,and predominant frequency range of subgrade surface is further expanded than that before bonding.The vibration acceleration level of rail,ballast bed at different positions and the surface layer of subgrade bed is mainly enhanced in different frequency bands,while the sleeper has obvious damping effect in the frequency band above 315 Hz.(3)The existing constitutive model of ballast bonding is modified,and four kinds of bonding modes are proposed,and the corresponding constitutive models are established.On this basis,the discrete element model of glued ballast bed is established and verified.The interaction modes of sleeper-glue-ballast and ballast-glue-ballast are studied.Based on the analysis of two types of actual bonding spots,four types of bonding modes of ballast glue are determined,which are ballast-ballast contact bonding,ballast-ballast separation bonding,ballast-sleeper contact bonding and ballast-sleeper separation bonding.Based on the comprehensive consideration of the distribution of ballast glue in the ballast bed,the characteristics of the ballast bed,and the physical meaning of the bonding of ballast glue at the meso level,the corresponding bonding constitutive models are established for four different bonding modes.On this basis,the full-scale discrete element model of sleeper ballast bed and the discrete element model of ballast box are established by using the discrete element method,and the meso parameters of the model are calibrated and verified by combining with the field test results.(4)The full-scale discrete element model of sleeper-ballast bed is used to analyze the resistance evolution characteristics of glued ballast bed.The resistance sharing mode is revealed and the influence of ballast glue bonding defects and bonding mode on ballast bed resistance is analyzed,and further realize the bonding mode optimization of glued ballast bed.Based on the full-scale discrete element model of sleeper track bed,the transfer mode and sharing characteristics of the resistance load when the sleeper moves laterally or longitudinally are analyzed.The bond defects of ballast glue and the influence of the bonding mode of ballast bed,including single curing mode and comprehensive curing mode,on the resistance evolution of ballast bed are revealed,and the bonding mode of ballast glue is optimized.The results show that: for the lateral resistance,the ratio of the crib,the bottom,the shoulder on the side facing the sleeper and the shoulder on the side back the sleeper changes from large to small;For the longitudinal resistance,the order of the sharing ratio of different positions of the ballast bed from large to small is the crib on the side facing the sleeper,the bottom,the crib on the back side facing the sleeper and the shoulder.The main sources of ballast resistance sharing are sleeper-ballast compression contacts and sleeper-ballast contact bond point.The influence of bonding defect state of sleeper ballast contact point on the lateral resistance attenuation is stronger than that on the longitudinal resistance.According to the envelope line of the optimal bonding mode,the optimal matching of the ballast glue dosage,bonding mode and the ratio of resistance increase of the ballast bed can be realized.(5)Based on the discrete element model of the ballast box,the energy state and the evolution of macro and meso properties of the glued ballast bed under the action of highspeed train load are studied,and the inherent nature of its macro and meso mechanical properties is revealed from the perspective of energy.The evolution characteristics of different energy forms in the glued ballast bed under cyclic load of high-speed train are analyzed by using the ballast box model.The energy state corresponding to the meso contact characteristics and macro settlement deformation of the glued ballast bed is investigated.The results show that the elastic strain energy is always the most important energy form,followed by viscous strain energy,friction energy and damping energy.Compared with the common ballast bed,the glued ballast bed has more contact points,smaller contact force and more uniform energy distribution.The kinetic energy evolution of glued ballast bed has the characteristics of small amplitude and fast convergence,which reflects that the settlement deformation of glued ballast bed presents a similar law.