Research On Rational Stiffness Of Buffer Layer Of CRTS Ⅲ Slab Ballastless Track For Mixed Passenger And Freight Railway

Ballast track is generally used in mixed passenger and freight railway,and ballastless track is only used in the long tunnel section to reduce the maintenance work.So far,there has been no successful experience that it applies the ballastless track for the whole passenger and freight railway.In order to reduce the prominent problem of ballast track in high-speed and high-density railway transportation,the research and development of ballastless track has become an important development direction.In this paper,the structure of the CRTS Ⅲ slab ballastless track is improved,the 4～8mm thick buffer layer is set up to replace the original isolation layer between the self-compacting concrete and the base plate,which is used to absorb the deformation and vibration of the upper structure,and has the function of buffering,isolating and providing certain elasticity.In addition,the stiffness of the fastener,the thickness of the track slab and the base plate are added to improve the bearing capacity of the track structure,and finally,the ballastless track which is suitable for the lighter axle freight and the high-speed passenger line is formed.First of all,according to the structure of CRTSⅢ slab track of mixed passenger and freight railway,a three-dimensional solid model is established by using the finite element method,then,the transient dynamic method is used to analyze the deformation and stress of the track structure,the results show that:the CRTS Ⅲ slab track with buffer layer can effectively reduce the deformation of the fastener and the vertical force of the base plate,not only relieves the dynamic action between the self-compacting concrete and the base plate but also can better protect the fastener,the self-compacting concrete and the base plate;it is suggested that the fastener stiffness of the CRTS Ⅲ slab track is taken as 60kN/mm,and the surface stiffness of the buffer layer is 300-400MPa/m for mixed passenger and freight railway;by compared with the ballast track,it is shown that the effect of the buffer layer of the CRTS Ⅲ slab track is similar to the ballast,which provides reasonable flexibility for ballastless track.Secondly,considering the influence of train load,temperature gradient and uneven settlement of subgrade,this paper analyzes the structural stress of CRTS Ⅲ slab track of mixed passenger and freight railway,the results show that:the strength of each component of the track meets the strength requirements,and the tensile and compressive stress of the track slab and self-compacting concrete is slightly bigger under the load of passenger,but it is little difference;then this paper uses the collision to simulate the flap action between self-compacting concrete and the base plate,the buffer layer can alleviate the impact of the flapping action on the layers of the track structure under the condition of the seam,which effectively reduces the contact force.Finally,based on the dynamics of vehicle-track system,the vertical coupling model of the vehicle and CRTS Ⅲ slab track for mixed passenger and freight railway is established,then this paper studies the influence of the stiffness of the buffer layer and the fastener on the structural stress of the ballastless track,the following conclusions are obtained:adopting the way of subgrade transition can effectively realize the uniform stiffness transition of the subgrade and tunnel junction,which can meet the requirements of track smoothness and stability;in this paper,it is suggested that the transition section between subgrade and tunnel should adopt the way of subgrade grade transition,and the transition length is the length of four track slab and the stiffness of the subgrade surface are 300,500,750,1000MPa/m.