Experimental and Numerical Verification of the Railway Track Substructure with Innovative Thermal Insulation Materials

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.

Recent studies on railway-track substructure at TTCI

Railway-track substructure is the foundation of the railway-track infrastructure and consists of four major components: ballast, sub-ballast, subgrade and drainage. Safety and performance of the track infrastructure, to a large degree, depends on the performance of the track substructure. Adequate support from the track substructure is the most critical element needed for good track performance. When properly constructed and maintained, the ballasted track is the most cost-effective track structure for railway operations, especially for heavy-haul freight operations. Good track-substructure support is characterized by good drainage and strong resistance of the ballast, sub-ballast and subgrade layers to excessive deformation and failures under repeated dynamic wheel loads. As the track substructure plays such important roles, research concerning track substructure has been broad and extensive around the world, with many universities and research institutes conducting various studies and investigations. This paper provides an overview of the recent research conducted at Transportation Technology Center, Inc. (TTCI), a subsidiary of the Association of American Railroads (AAR), in the following areas: ballast mud pumping and its effects on track performance, remediation of subgrade mud pumping, remediation of ballast pockets, ground-penetrating radar (GPR) for inspecting track substructure, and development of software tools with focus on track-substructure functions and management.

Railway infrastructure in earthquake affected areas

In the case o seismic impact on rail infrastructure, even small deformations or damage to track structure can compromise safe operation of rail traffic. Damage can affect track substructure or permanent way of the track, but also the electrification system and safety-signalling devices. Ballast prism will suffer damage in case of greater intensity earthquakes, resulting in the reduction of lateral and longitudinal resistance of track structure. Earthquake action may also cause derailment of moving rail vehicles. Operation of rail vehicles also causes certain levels of vibrations, and so an analysis of subsequent effects of rail traffic.

TESTING THE SUITABILITY OF THE EXTRUDED POLYSTYRENE (STYRODUR) APPLICATION IN THE TRACK SUBSTRUCTURE

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).