Research On The Characteristics Of Flow Movement And Erosion In The Gap Of Ballastless Track

In the operation process of ballastless track,various kinds of damage will inevitably appear in the track structure due to some complex factors such as train load,temperature changes and rainwater infiltration,the more typical ones are the gap and grout oozing out.When rainwater enters the gap between slab and supporting layer,the load of the train will produce dynamic water velocity and pressure.The velocity will produce shearing stress on the concrete surface,and the water pressure will produce tension and compression stress.When the above stress destroys the connection force between the concrete particles,the particles will be separated from the matrix,and the separated particles will move with the fluid,causing erosion on the concrete surface,and the concrete particles will detach again,forming void and other serious diseases,seriously affecting the safety and stability of driving,and reducing the life of the track structure.Therefore,to carry out the research on the water movement characteristics and erosion mechanism of the gap of the ballastless track has important reference significance for the maintenance and repair of the ballastless track.In this paper,a model experiment of water flow velocity measurement was carried out,a finite element calculation model for the velocity of the gap was established,and a finite element detailed erosion model of the gap considering the rough surface of concrete was established,a series of studies on the characteristics of water flow distribution and erosion action in the gap of concrete were carried out by combining theoretical calculation with experimental measurement.Firstly,this paper designed a model experiment for measuring the water flow velocity in the gap of concrete,based on the principle of pitot tube to measure the velocity of water,proposed a method for measuring the water flow velocity in the gap of the ballastless track,designed the assembly steel plate tooling of the model experiment,and the different points between the gap of dynamic water flow speed were measured.Then,Based on the theory of fluid-solid coupling,a finite element calculation model for the velocity of the gap was established,and compared with the measured results,the results show that the maximum flow velocity at the opening from the gap,the minimum at the end,and the flow velocity changes rapidly near the opening;the flow velocity is affected by various factors such as loading frequency,loading amplitude and height of the gap;the distribution trend of the measured values is basically consistent with the calculated values,the fluid-solid coupling calculation model established in this paper can be used to evaluate the dynamic water velocity distribution characteristics in the gap of concrete under dynamic load.Finally,Based on the theory of solid-liquid two-phase flow and erosion,a finite element erosion model of the gap considering the rough surface of concrete was established,and the particles movement characteristics and erosion mechanism were explored.The results show that,the trajectory of the particles is mainly affected by the fluid velocity and the height of the gap;at the position of the highest roughness peak,the particles collide with the concrete wall the most;the maximum erosion rate occurs at the position of the highest roughness peak and is affected by various factors such as the flow velocity,height of the gap and the particle concentration;shear stress is the main reason caused the concrete erosion of the gap of ballastless track;the relationship between the erosion rate and the distance to the opening is quadratic.