Abstract
A method for calculating impairment of the track geometry under influence of dynamic loads in the course of passing the track unevenness by the rolling stock was developed. The method takes into consideration interrelated short-term processes of dynamic interaction and long-term processes of subsidence of the ballast layer in a mutual influence on each other. Mathematical model of dynamic interaction of the track in the form of a planar three-layer continual beam system with a two-mass discrete system corresponding to the rolling stock is the basis of the first part of the method. This model makes it possible to simulate dynamic loads from individual sleepers to the ballast when the rolling stock passes geometric unevennesses and the track elasticity unevennesses.The second part of the method is based on the phenomenological mathematical model of accumulation of residual deformations formed using the results of laboratory studies of subsidence of individual sleepers in the ballast layer. Peculiarity of this model consists in taking into consideration not only uniform accumulation of residual subsidence from the passed tonnage but also presence of a plastic component of subsidence which depends on the maximum stresses in the history of ballast loading by each sleeper.A new theoretical mechanism of development of the track unevenness was proposed. It takes into consideration not only residual subsidences of the ballast layer but also appearance of gaps under sleepers resulting in a local change of the track elasticity. This mechanism enables taking into consideration the ambiguous influence of subsidences with occurrence of gaps under the sleepers. Subsidence causes an increase in dynamic loads on the track and the ballast layer on the one hand and onset of the gap causes a decrease in the track rigidity and corresponding reduction of dynamic loads on the other hand.Practical application of the developed method was demonstrated on an example of quantitative estimation of long-term uneven subsidences of the ballast layer when changing the sleeper diagram
Highlights
Two fundamentally different types of tracks are used on the world railways: with a ballast layer and with a ballast-free base
Uneven subsidence of the ballast layer caused by high dynamic loads from the rolling stock leads to impairment of the track geometry which further influences lifecycle of all elements of the track
The shape of subsidence unevenness for various numbers of passed axles is obtained. It was shown in [3] that variable rigidity of the lower track structure plays a decisive role in impairment of the track geometry since, on the one hand, it leads to an increase in dynamic loads from wheels on the track and, on the other hand, it is a direct cause of uneven subsidence of the ballast layer and the ballast bed
Summary
Two fundamentally different types of tracks are used on the world railways: with a ballast layer and with a ballast-free base. Uneven subsidence of the ballast layer caused by high dynamic loads from the rolling stock leads to impairment of the track geometry which further influences lifecycle of all elements of the track. Uneven subsidence of the ballast layer depends on many factors of the upper structure of the track, properties of the ballast bed, characteristics of the rolling stock, operating conditions and local atmospheric influences [1]. Growth of loads on the ballast layer may be caused by a series of factors the main of which is growth of dynamic loading from the rolling stock in the event of the track unevenness Another factor relates to the occurrence of gaps under the sleepers, that is, a total or partial loss of backing of the sleepers on the ballast. The methods based on phenomenological models [3, 8, 9,10,11] do not take into consideration influence of the rolling stock and the track factors they enable prediction of the track geometry impairment
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