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.

A new automatic measurement system for high-speed railway substructure settlement based on hydrostatic pressure difference levelling

Exact settlement measurement of substructures plays an important role in their status detection throughout all-life-cycle of high-speed railway. A Hydrostatic Pressure Difference Levelling system (HPDL) is developed based on the mechanism that pressures of any two points at different elevations in incompressible static liquid are different. The approach accounts for a hyperbolic variation in the density of the pressure transmission liquid with temperature, variation in the earth’s gravitational field and the elevation at the measurement point. High accuracy capacitive differential pressure transmitters are adopted owing to their high sensitivity, temperature-insensitive, low energy consumption, and sensing stability. The HPDL results are verified with settlement values measured by the precise level. It was demonstrated that the HPDL results correlate well with the precise level and can be considered as an effective method to measure the settlement of high-speed railway substructures.

Degradation modelling of railway infrastructure

<p>In this paper the Wiener process with linear drift is proposed as a degradation model for the railway substructure. The model is based on the empirical data describing loss of tracks quality over the distance of one kilometre. The impact of explanatory variables on tracks degradation is investigated. The Bayesian framework is applied to examine uncertainty in the development of degradation for different sections along the tracks.</p>

Application of seismic tomography for assessment of the railway substructure condition

This article presents results obtained in the research conducted on railway infrastructure in Serbia, which aimed at prediction of substructure condition based on the analysis of track quality. It presents the results of seismic tomography application as non-destructive procedure for assessment of railway substructure condition. Track geometry quality was assessed according to analysis of longitudinal level data, which was recorded during regular track geometry inspections. Track section for application of seismic tomography was chosen on the basis of analysed track geometry data recorded during the regular track geometry inspections in 2006, 2008, 2009, 2012, 2013 and 2014. Tomographic imaging of railway platform on Test Section enabled the creation of two-dimensional finite element model, which was used for determination of propagation speed of seismic P-waves. Seismic tomography on Test Section, which is the part of the international railway line Belgrade–Vrbnica, was performed in 2014. Obtained tomographic image was discussed and compared to track geometry data recorded during the regular track geometry inspections.

Utilization of ash from power plants for high embankments on soft soil

The ash landfills are a major environmental issue. The use of ash for the highway and railway substructure achieves a double benefit: it significantly reduces the deposited quantities of ash as well as the consumption of natural materials such as crushed stone, gravel and sand. The investigation of engineering properties of fly ash from the power plant in Serbia was conducted at the Laboratory of Soil Mechanics at the Faculty of Civil Engineering in Belgrade. Relevant physical and mechanical properties of ash and mixtures with binders (cement/lime) were investigated. The ash was also tested from the aspect of the potential environmental impact, which primarily depends on the leaching behaviour of the present trace elements. The results of the study showed that fly ash meets technical and environmental requirements and that has the potential for use in highway substructure, such as construction of embankments and stabilization of soft soils. Benefits of utilization of ash and slag was shown in the case of the construction of a high embankment on soft soil on the highway section Obrenovac-Ub in Serbia.

COMPARATIVE ANALYSIS OF BEARING CAPACITY OF REINFORCED AND NON-REINFORCED RAILWAY EMBANKMENT

A comparative analysis using the programme ANSYS (FEM) deals with the generation of the computation model and with the assessment of the influence of the geogrids and the vertical lime-cement columns on the bearing capacity and deformation of the railway embankment on the less load-bearing subsoil. The graphic outputs give an overview of the field layout of equivalent stresses and deformation in the construction of the railway substructure.