Abstract
This paper compares methods of designing the track bed structure that are used in the processes of design and review design of subgrade tracks located in Slovakia and Lithuania. Self-comparison is made on a particular type of track bed with the aim to highlight the differences between individual countries methodologies that affect not only the dimension of the sub-ballast layer, but also economic demands and reliability of the design of railways structure.
Highlights
The railway of a rail vehicle, that consists of rails, sleepers, track fittings, ballast bed, the body of the subgrade and its objects, must be sufficiently deformation-resistant and must adequately resist the effects of a number of negative operating factors (Bai, Liu, Sun, Wang, & Xu, 2015; Navikas, Bulevičius, & Sivilevičius, 2016)
As it is clear from the comparison of the design methodologies used in Slovakia and Lithuania on dimensions design of the sub-ballast layer of a track bed (TB), the draft design of the subbase layer thickness that is based on the dimensioning of the TB structure for traffic load, in general, for the tracks of Lithuania its smaller structural thickness is calculated if compared to the thickness of the subbase layer based upon the prescribed methodology used in Slovakia, namely it is the structural thickness of 0.25, or 0.20 m (LG) compared to 0.20–0.50 m (ŽSR)
What is essential is the fact that, for example, the values of the thermal conductivity coefficient (λ) for material of the ballast bed – track ballast – as stated for the process of structure dimensions designing of the subballast layer for railway tracks administered by ŽSR and LG are very different, which in turn has a major impact on the thermal resistance of the structural layer of the ballast bed, and the zero isotherm penetration into the structure of the railway track
Summary
The railway of a rail vehicle, that consists of rails, sleepers, track fittings, ballast bed (that together form the railway superstructure), the body of the subgrade and its objects (that together constitute the track substructure), must be sufficiently deformation-resistant and must adequately resist the effects of a number of negative operating factors (Bai, Liu, Sun, Wang, & Xu, 2015; Navikas, Bulevičius, & Sivilevičius, 2016). Static and dynamic load altogether compose the so-called transport railway track loading (AB “Lietuvos geležinkeliai” [LG], 2013; Directorate General of the Railways of the Slovak Republic, 2005) In addition to these direct loading effects by rail vehicles the structure of the railway track is being exposed to other effects, to weather and climate actions (water, frost, solar radiation and wind) causing thermal effects of rail strings and changes in the thermal conductivity regime of the subgrade surface (Yang et al, 2015; Ižvolt, Dobeš, & Pultznerová, 2016).
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