Railway Granular Ballast Resistance Evolution Mechanism And Its Influence On Continuous Welded Rail

The ballasted bed is the main carrier for supporting the track frame and maintaining the stability of the track structure.With the development and application of CWR(continuous welded rail)technology,the value of the ballasted bed resistance and its distribution,which is closely related to line stability,rail crawling,rail layout and design of CWR on the bridge,has always been the focus and hotspot of railway researchers in all countries.However,based on the influences of diversity,periodic loading form,dynamic live load and special environmental conditions,the longitudinal supporting and force transmission mechanism of the ballasted is extremely complicated,and the ballasted bed resistance distribution exhibits discrete,random and strong nonlinear characteristics.The study on the longitudinal and lateral resistance characteristics and variation of ballasted track during dynamic service process,has become the foundation of understanding dynamic behavior,stability mechanism of ballasted track and mechanical deformation mechanism of CWR deeply.Therefore,this paper focuses on the longitudinal and lateral resistance performance of the ballasted bed and its influence on the mechanical deformation mechanism of CWR.The experimental research and theoretical analysis are carried out as follows.1.Nonlinear macroscopic characteristics of the ballasted bed resistance and the simulation of its dynamic evolution behaviorCombined with the structural characteristics and mechanical properties of the ballasted track,the intensification,attenuation,degradation characteristics and production mechanism of the ballasted bed resistance are analyzed;A ballasted bed dynamic resistance test system was developed,which can be used to analyze the characteristics of the resistance-displacement curve of the ballasted bed and other characteristics under different load conditions2.Track frame nonlinear resistance and its influence on CWRBased on the longitudinal force transmission characteristics of the track and the ballasted bed in the CWR expansion and contraction section,the turnout,and the CWR of the bridge,the nonlinear longitudinal resistance of the ballasted bed influenced by the track framework can be obtained;In the meanwhile,to build the track framework based on the absolute displacement of the sleeper and the relative displacement of the bolster,an iterative algorithm is proposed.When the track frame is introduced into the beam-rail mutual analysis model,it can be found that the resistance of the track frame will alleviate the beam-rail interaction in the expansion and contraction section and flexure conditions,causing a significant reduction in the contractility and flexural forces of the rail.As a result,the longitudinal force transmission performance of the ballasted bed is overestimated in the existing analysis of the beam-rail interaction on the bridge.With the utilization of track skeleton model,the characteristics of the resistance-displacement curve of the ballasted bed under repeated loading and unloading are analyzed by using the repeated loading and unloading test of equal displacement increment.It turns out that the accumulation of residual plastic deformation under repeated loading and unloading affects the force transmission capacity of the ballasted bed.That's to say,the longitudinal supporting capacity of the ballasted bed increases under the same displacement conditions.On the basis of the experiment,the force and deformation law of the continuous welded turnout is simulated and analyzed under the repeated loading and unloading of the train on the slope.It turns out that the rail crawling phenomenon is obvious under repeated loads.3.Ballasted bed deformation characteristics under cyclic loadingWith the utilization of the ballasted bed dynamic resistance test system,the ballasted bed resistance-displacement hysteresis curve under cyclic loading can be obtained,of which morphological characteristics and variation law of various characteristic parameters are analyzed at the same time,together with the evolution law of resistance performance of ballasted bed under dynamic reciprocating load.It can be concluded that the unloading curve of the ballast bed under cyclic loading does not coincide with the loading curve,but the two curves form a closed hysteresis curve,which reveals there is a obvious energy consumption.The deformation characteristics of ballasted bed and morphological characteristics of hysteresis curve are not in an ideal state.The parameters such as the elasticity,plasticity and energy dissipation capacity of the ballasted bed are affected by the cyclic displacement amplitude and loading rate;After the ballasted bed is subjected to continuous dynamic reciprocating disturbance,the longitudinal and lateral resistance of the ballasted bed exhibits degenerative characteristics which are closely related to the amplitude of the cyclic disturbance displacement.4.Ballast resistance evolution characteristics on bridges and its influenceIn allusion to the ballasted bed in the special section on the bridge,the deformation characteristics of the ballasted bed are studied under the cyclic loading of the temperature and the low-frequency vibration load of the train.It turns out that the liquefaction flow of the ballast accumulation is one of the main inducements to attenuate the resistance of the ballasted bed.Moreover,it can also lead to defects such as insufficient supporting capacity of the track structure and deterioration of the geometrical state of the rail level.Based on the facts above,the distribution characteristics of the resistance of the ballasted bed on the bridge are proposed.It is found that the deteriorating of ballasted bed resistance will make it larger for the beam-rail interaction results calculated according to the existing specifications.Meanwhile,the stability of the ballasted bed on the large span flexible steel bridge,along with the migration and rheological behavior of the ballast is analyzed.It is recommended that to improve the structural adaptability and stability of the ballasted bed on the bridge,structural strengthening measures should be adopted.5.Ballast resistance characteristics in low temperature freezing environmentAfter the construction of a low temperature environmental test chamber with a ballasted bed,the longitudinal and lateral resistance performances of the ballasted bed under different temperature conditions and different states(freezing or not)were analyzed,and the resistance evolution of the ballasted bed under different environments is obtained.It can be found that the changes in the physical parameters of the particles in a low temperature environment will attenuate the resistance performance of the ballasted bed;Train dynamic load can destroy the bonding state of particle contact surface under low temperature with freezing,it is an unstable supporting state when the surface of the particles is covered with a layer of ice membrane due to the low temperature,which weakens the friction,self-locking behavior of the ballast and leads to the degradation of the ballast force transmission performance.The research results provide experimental data support for the development of key technologies for the ballasted bed in CWR in frigid areas.