Analysis On The Influence Of Unsupported Sleeper And Regulation Operation On The Mechanical Properties Of Railway Ballasted Bed

As one of the common problems in ballasted track,unsupported sleeper will change the stress characteristics of ballast particles and the supporting stiffness under the sleeper.Therefore,when the train passes through the unsupported sleeper section,the wheel rail force and the settlement of track bed will increase,which will change the dynamic response of ballast bed,aggravate the deterioration of sleeper,fastener system and ballast,and seriously affect the driving safety.Therefore,aiming at the problem of unsupported sleeper in railway lines,firstly,this paper investigates the current situation of unsupported sleeper.Secondly,the influence of unsupported sleeper on the dynamic characteristics of ballasted track and the influence of unsupported sleeper on the dynamic stability of ballasted bed are analyzed,Finally,in order to improve the problem of unsupported sleeper in ballasted track line,the improvement effect of tamping and stabilizing operation on the quality state of unsupported sleeper ballasted bed is studied by discrete element method.The main research contents and conclusions are as follows:(1)The wheel rail dynamic model is established,and the influence of unsupported sleeper on ballasted track structure is studied from three aspects:the number of unsupported sleeper,speed and axle load.The results show that when sleeper unsupported,the dynamic response of rail will be significantly amplified,and the continuous unsupported of three sleepers has the most significant influence on ballasted track structure;When the speed is 120 km/h,the dynamic response of track structure is the most significant under the action of 28t axle load.Under this condition,the maximum vertical vibration acceleration of rail and sleeper are432.86m/s~2 and 237.28m/s~2 respectively.(2)Aiming at the common problem of unsupported sleeper in ballasted track,the influence of unsupported sleeper on the dynamic stability of ballasted track bed is studied from two aspects:the state of unsupported sleeper and the number of unsupported sleeper.The results show that the unsupported sleepers will increase the difference of ballasted bed quality between the two adjacent sleepers,resulting in serious differences in the stress conditions of the two adjacent sleepers and aggravate the aging of sleepers;When the sleeper is continuously unsupported,the vibration damping performance of ballasted bed in the frequency range of 0～450Hz is better than that in the high frequency range.(3)The best treatment measure of unsupported sleeper is tamping operation.Therefore,the discrete element model of ballasted bed is established to study the impact of tamping operation on the quality state of unsupported sleeper ballasted bed.The results show that when tamping the unsupported sleeper ballasted bed,the vibration amplitude of the tamping pick is recommended to be 7mm,the vibration frequency of the tamping pick is recommended to be35Hz,the insertion depth of the tamping pick is recommended to be 15mm,and the insertion speed of the tamping pick is recommended to be 1.6m/s;After tamping with the best tamping operation parameters,the lateral resistance of ballasted bed is 4.95k N,the supporting stiffness under the sleeper is 44.23k N/mm,and the average compactness under the sleeper is1615.54kg/m~3.(4)After the tamping operation is completed,conduct stable operation on the unsupported sleeper ballasted bed,and the influence of stable operation on the quality state of unsupported sleeper ballasted bed is studied.The results show that among the parameters of stable operation,the vertical downward pressure and horizontal excitation frequency have obvious effects on the quality of ballasted bed after stable operation.During stable operation,it is recommended to select 25k N for vertical downward pressure and 30Hz for horizontal excitation frequency;After stabilizing with the best stable operation parameters,the lateral resistance of ballasted bed is 6.72k N,the supporting stiffness under the sleeper is 82.64k N/mm,and the settlement of sleeper is 2.16mm.