Verification of boundary conditions of numerical modeling of the track substructure thermal regime – influence of the snow cover

Abstract

The initial part of the paper briefly characterizes a long-term experimental activity at the Department of Railway Engineering and Track Management (DRETM). The research of the DRETM focuses, besides other research activities and specific problems in the field of railway engineering (application of new structures and construction materials in conventional and modernized railway tracks, modernisation and rehabilitation of existing railway tracks for higher speeds, track diagnostics, influence of track operation on noise emissions and design of structural measures, possibility of application of recycled ballast bed material in the track substructure, ballast recycling technologies, ecological assessment of recycled material of the track substructure), on various factors affecting track substructure freezing. In 2012-2017, in the campus of the University of Žilina (UNIZA), an Experimental stand DRETM was built for the research purposes. The experimental stand DRETM consists of 6 types of track substructure placed in an embankment or a cut, in the 1:1 scale. Besides conventional building materials (crushed aggregate), these structures also include various thermal insulation materials (Liapor concrete, Styrodur, foam concrete). A significant part of the paper deals with numerical modeling of the freezing process of track substructure (an embankment with the embedded protective layer of crushed aggregate, fr. 0/31.5 mm) for various boundary conditions (air frost index, average annual air temperature), using SoilVision software. The aim of this research is to identify the thermal insulation effects of different thicknesses of snow cover on the depth of penetration of the zero isotherm into the track substructure (railway track). The paper conclusion specifies the influence of different snow cover thicknesses, or nf factor (factor expressing the dependency between the mean daily air temperature and the temperature on the ballast bed surface) and various climatic conditions (frost indexes and average annual air temperatures), affecting the railway infrastructure, on the resulting depth of freezing of the track substructure (railway track). These outputs will be in the further research used for the design of nomogram for determining the thickness of the protective layer of the frost-susceptible subgrade surface of the track substructure.

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

“…The difference between the values determined by the experimental and numerical methods is 0.002 m, which is a negligible difference with respect to the methodology of design of the structural sub-ballast layers of the railway line [ 100 ]. Moreover, the obtained accuracy of recreating the measurement results in the numerical model is the same as for other railway track substructure–subsoil systems [ 7 ] and consistent with previous observations [ 109 ]. Therefore, the model can be considered validated.…”

Protection of Structural Layers of Transitions Zones on Railways against Freezing, Using Materials with a Low Coefficient of Thermal Conductivity

“…The SV-HEAT allows for these experiments and calculations, which are based on finite element calculations (formulas and calculations are part of company materials under copyright). The SV-HEAT was verified by previous research tasks and was mainly compared with the built in situ models of the heavy laboratory of the Department of Railway Engineering (DRE) by Hodas et al [9]; Izvolt, Dobes and Hodas [10]; Izvolt, Dobes and Pies [11]; and by Sestakova and Dobes [12].…”

Assesment of the Possibility of Foam Glass Application in the Sub-Ballast Layers

“…In the numerical models, a value of nf = 0.6 (the value attributable to the thickness of the snow cover aligned to the top surface of the ballast bed) was used during the winter period. The influence of snow cover thickness on the nf factor values was presented in Ižvolt et al (2018). -10 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 The calculation of the freezing of the structural layers of the railway track in numerical models was performed using the FlexPDE programme and the ACU-MESH programme was used to visualize the solution results (Fredlund & Haihua, 2011).…”