The article aims to present the modified structural composition of the sub-ballast layers of the railway substructure, in which a part of the natural materials for the establishment of sub-ballast or protective layers of crushed aggregate is replaced by thermal insulation and reinforcing material (layer of composite foamed concrete and extruded polystyrene board). In this purpose, the experimental field test was constructed and the bearing capacity of the modified sub-ballast layers’ structure and temperature parameters were analyzed. A significant increase in the original static modulus of deformation on the surface of composite foamed concrete was obtained (3.5 times and 18 times for weaker and strengthen subsoil, respectively). Based on real temperature measurement, it was determined the high consistency of the results of numerical analyses and experimental test (0.002 m for the maximum freezing depth of the railway line layers and maximum ±0.5 °C for temperature in the railway track substructure–subsoil system). Based on results of numerical analyses, modified railway substructure with built-in thermal insulating extruded materials (foamed concrete and extruded polystyrene) were considered. A nomogram for the implementation of the design of thicknesses of individual structural layers of a modified railway sub-ballast layers dependent on climate load, and a mathematical model suitable for the design of thicknesses of structural sub-ballast layers of railway line were created.

This article presents the authors’ comprehensive evaluation of the application of specific foam thermal insulation materials, namely expanded polystyrene (EPS) and extruded polystyrene (XPS), within railway substructures. The assessment extends to real-world conditions on the tracks of Slovak Railways (ŽSR), which share substantial similarities with other countries’ railway networks. The assessment of structural composition and material selection considers these technical aspects, while technological feasibility and the environmental implications associated with material production, delivery, and incorporation into railway construction do not. Additionally, the thermal insulation materials’ qualities are compared against conventional railway substructure materials. In these conventional setups, the thermal insulation layer often incorporates crushed aggregate of specified fractions and parameters in line with legislative standards. This article complements previous research conducted at the University of Žilina, focusing on the application of various thermal insulation materials within railway substructures. These materials were both experimentally tested (scale of 1:1) and numerically modelled, with results previously published by the authors. The published works detail the utilisation of diverse thermal insulation materials in railway substructures, primarily evaluating two crucial technical parameters: the protection of the subgrade surface against adverse effects of frost and, secondarily, their impact on the deformation resistance of the railway substructure.

Most of the railway lines in Slovakia were built in the second half of the 19th century, or until 1918 (the establishment of Czechoslovakia). Except for the post-World War II period, when approximately 71 % of the Slovak lines had to be renewed, limited funds have been spent on repair and reconstruction works on the lines located in the Slovak territory. As some trans-European corridors cross the Slovak territory and the Slovak Republic assumed obligations arising from the AGC and AGTC agreements, the line modernization is more than desirable. The primary objective of the modernisation of railway lines in the territory of Slovakia is to ensure a high-quality and safe railway, which by its qualitative parameters corresponds to the standards of developed European countries. In this context, the paper deals with a section of the modernised corridor no. Va, specifically the section Považská Teplá - Žilina. During the period 2014-2017, quality diagnostics of the performed work was carried out on the sub-ballast layers of the above-mentioned line. Consequently, we carried out an analysis of the obtained values of the deformation resistance of the subgrade surface, as the weakest element in the construction of the sub-ballast layers.

This paper presents the results of numerical modelling of the influence of various factors (geometrical layout of the structural layers of the railway track, climatic factors and ballast fouling) on the freezing of railway track structure with a built-in thermal insulation layer of extruded polystyrene (Styrodur). At the same time, the suitability and expediency of incorporating the thermal insulation layer at the sub-ballast upper surface level (i.e. below the rail ballast construction layer), or at the level of subgrade surface are discussed. Numerical modelling results in the main factors that should be taken into account in the dimensioning of the sub-ballast layers with a built-in thermal insulation layer. Based on the data on the depth of freezing of the railway track structure obtained from numerical modelling, a design nomogram for dimensioning was created and subsequently the influence of the changes of climatic characteristics on the freezing of the railway track structure was then mathematically expressed.

Extruded polystyrene (XPS) and its excellent thermal insulation properties have been known for over 60 years. Due to its thermal, mechanical, but also deformation properties, XPS has a universal application, not only in the construction industry. This paper presents the results of the first series of experimental measurements of the deformation resistance of the sub-ballast layers with a built-in XPS thermal insulation layer and the sub-ballast layers with a standard structure (crushed aggregate sub-ballast layer). The aim of the first series of experimental measurements was to determine the impact of placing the XPS layer at the subgrade surface level (deformation resistance of subgrade surface E0 = approx. 10MPa or 30MPa) on the deformation resistance of the sub-ballast layers and then to determine the necessary thickness of the sub-ballast layer in relation to the required deformation resistance at the sub-ballast upper surface. Experimental measurements carried out so far show that the application of XPS boards in the sub-ballast layers has almost no or minimal effect on its deformation resistance. Since XPS boards have significantly better thermal technical properties compared to crushed aggregate, considerable savings of this material can be achieved in areas with unfavorable climatic conditions (high values of air frost index).

The paper focuses on the analysis of the values of the static modulus of deformation obtained by the application of the test procedure specified in the methodology for the diagnostics of the sub-ballast layers used for German railways (DIN 18 134) and the Railways of the Slovak Republic (Regulation TS4). The purpose of the study was to determine the correlation between the measured values of the static modulus of deformation according to the above-mentioned methodologies based on a series of experimental measurements on an experimental field built at a scale of 1:1. It also aimed to develop a numerical model characterising the behaviour of the loaded environment during the experimental measurements using the finite element method, which can subsequently be used for the design of the structural composition of the sub-ballast layers. For the purpose of the experimental measurements, a sub-ballast layer of 0/31.5 mm crushed aggregate of different design thicknesses was applied to the sub-ballast layers. A polynomial dependence with a high value of the reliability coefficient can be found between the results of the static modulus of deformation obtained using the mentioned measurement methodologies during the quality inspection of the implemented construction works. This dependence is valid for the specific boundary conditions of the experimental measurements performed (subsoil of clay with gravel admixture and the sub-ballast crushed aggregate layer of 0/31.5 mm dolomitic gravel). In the future, establishing correlation dependencies for other boundary conditions and structural material compositions can be considered.