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Track Geometry

Methods

Emphasis on quality of track work and a thorough knowledge of the tracks service condition provides for a track which is predictable and reliable. Track geometry condition is a key aspect of this maintenance approach.

The mechanism governing the phenomenon of track deterioration is rather complex. If a track is freshly tamped it is well-known that directly afterwoods, relatively large settlements occur. If every point of the track were to settle by the same amount no irregularities would develop.

However, these settlements are often far from uniform due to in homogeneities in support conditions, track structure and load distribution.
 
 This results in differential settlements which lead to the development of irregularities in the wavebands experienced by the rolling stock.
 
 To confine track deterioration, it is of great importance to keep geometrical irregularities as small as possible, starting directly at the renewal, and to confine layer thickness variations during track renewal and ballast cleaning.

Deterioration of the geometry is identified as having three main causes. random settlement of the ballast, arising from the ballast itself, or from variations in the stiffness of the foundation, lack of straightness of the rails and variation in the dynamic loads along the track caused by vehicles.

It was shown from calculations that the most significant dynamic loads could come from unsprung masses associated with wavelengths in the track of less than about 1 m.


It is an awareness of this dynamic environment which underpins the policies and strategies of many European railway operators.
 

The European's in formulating maintenance strategies ensure that much emphasis is placed on achieving quality targets through the use of appropriate and technically correct techniques. Over the last 20 years a number of tools have developed to facilitate the control of track geometry condition in line with this emphasis.



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