| The ballast track have granularity and combinability.The longitudinal and lateral resistance of the ballast bed is essential to ensure that the track panel remains stable within the ballast bed.Track panel in the form of sleeper group buried inside the ballast bed,together affect and contribute to the formation of the longitudinal and lateral resistance of the ballast bed,the evolution and stability of the track.The paper is combined with the case of AFUZHUN Railway project.In the big temperature difference area laying continuous welded rail(CWR)of ballast track,facing the rail temperature difference(maximum rail temperature difference112 ℃),rapid temperature changes(morning wear cotton jacket afternoon wear yarn),the existence of small radius curve(minimum radius R = 300 m),bridges(bridge 135)and large slope section(maximum slope 12.5 ‰)and other complex,harsh operating environment challenges.In order to study the applicability and safety of CWR of ballast track in this special and complex environment,the thesis establishes a sleeper group and ballast bed model for curved sections and a sleeper group and ballast bed model for large slopes on bridges based on the discrete element method.The relevant parameters were calibrated using the rest angle test and the resistance test,and the sleeper group-ballast bed model for curved sections and the sleeper group-ballast bed model for bridges with large gradients were carried out respectively.The study investigated the change law of ballast bed resistance and the law of ballast force transfer considering the sleeper group effect,and revealed the mechanism and influence of the sleeper group effect on ballast bed,for the problem of laying CWR with ballast bed in the area of large temperature difference and large slope,some measures to strengthen the stability of ballast bed were proposed and evaluated.The specific research contents of the paper are as follows.Based on the discrete element method,the ballast bed model was established,and the lateral resistance and the sub resistance of the ballast bed were compared under the change of the number of sleepers involved in the movement,and the change law of the ballast’s particle movement and contact characteristics were analyzed,and the causes and effects of the sleeper group effect were discussed.The effects of the sleeper group effect on the lateral stability of CWR were studied.The results show that the increase of the number of sleepers the ballast bed resistance is decaying trend,the number of sleepers from 1 to 3 when the most significant impact,after stabilization.The sleeper group effect under the ballast bed resistance decay mainly from the sleeper side and the sleeper end area,these two areas there are adjacent to the sleeper part of the common impact area of resistance,in the ballast body under the limited bearing capacity of the ballast bed resistance is then reduced.The simulation model of sleeper group and ballast bed in curved section is established,and the lateral force transfer characteristics of the ballast bed in curved section under the action of cyclic load are studied in terms of resistance curve,hysteresis performance and force transfer characteristics.The results show that,affected by the rapid cyclic action of large temperature difference load,the track panel is always in the process of cyclic reciprocal motion in the lateral direction,and the lateral resistance of the ballast bed has different degrees of attenuation.The degree of attenuation is related to the loading course and load size.When laying CWR under such special conditions,the effect of cyclic attenuation of the lateral resistance of the ballast bed should be considered in sections and areas,and it is appropriate to take the value of the stable lateral resistance of the ballast bed as calculation reference is more reasonable.A sleeper group and ballast bed model on a bridge with a large gradient is established,the influence of the ballast bed section size on the resistance and related characteristics is analyzed,the optimal value of the section size is discussed,and the change of the ballast bed resistance and force transmission characteristics under repeated braking of the train are studied from the aspects of resistance and force transmission characteristics.The study shows that the ballast bed resistance tends to intensify under different braking loads,and the smaller the braking displacement,the more braking cycles are required for the ballast bed resistance to stabilise.Compared to no-load conditions,the ballast bed reaches longitudinal stability more quickly when the train is repeatedly braked under loaded conditions.Based on the sub-resistance analysis,the longitudinal strengthening of the ballast bed is mainly caused by the densification of the ballast body between the crib.At the same time,repeated braking also results in a lifting of the sleeper displacement,a reduction of the sleeper bottom pressure,a reduction of the sleeper support stiffness,an increase of the geometrical unevenness and a sharp increase of the kinetic energy of the ballast body between the sleepers and a rheological phenomenon.Considering the actual operation of CWR in areas with large temperature differences,two types of ballast bed strengthening measures are proposed and their effects on strengthening the stability of the ballast bed are analyzed.The results show that the sleeper encryption can improve the overall stability of the ballast bed in the lateral and longitudinal direction,but will weaken the local stability of the ballast bed.The polyurethane local(sleeper core and sleeper end)curing can improve the lateral and longitudinal stability of the sleeper group,and it can be considered that this measure of polyurethane curing is more applicable to similar projects such as AFUZHUN Railway. |
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