Fractal analysis of track geometry data

ABSTRACT A Federal Railroad Administration sponsored research project has been ongoing to explore the use of Fractal Analysis of track geometry data for indication of track geometry roughness, maintenance planning and track substructure condition assessment. Fractal analysis provides unique numerical values (fractal dimensions) that characterize railway track geometry patterns. The fractal dimensions can be used for effective maintenance planning by providing meaningful parameters for geometry deterioration modeling, and by potentially providing information about the actual condition of the track by precise quantification of the geometry patterns. The paper will present a lucid discussion of fractal theory and will demonstrate its usefulness for quantifying railroad geometry data by highlighting key aspects of the research results. This paper also discusses the relationship between track structure conditions and fractal dimensions for use in maintenance planning and condition evaluation

New Transition Wedge Design Composed by Prefabricated Reinforced Concrete Slabs

[EN] Important track degradation occurs in structure-embankment transitions, in which an abrupt change in track vertical stiffness arises, leading to a reduction in passengers comfort and safety. Although granular wedges are suggested by different railroad administrations as a solution to avoid these problems, they present some disadvantages which may affect track long-term performance. In this paper, a new solution designed with prefabricated reinforced concrete slabs is proposed. The aim of this solution is to guarantee a continuous and gradual track vertical stiffness transition in the vicinity of structures, overcoming granular wedges disadvantages. The aim of this study is to assess the performance of the novel wedge design by means of a 3-D FEM model and to compare it with the current solution.Real Herráiz, JI.; Zamorano-Martín, C.; Real-Herraiz, TP.; Morales-Ivorra, S. (2016). New Transition Wedge Design Composed by Prefabricated Reinforced Concrete Slabs. Latin American Journal of Solids and Structures. 13(8):1431-1449. doi:10.1590/1679-78252556S14311449138Gallego Giner, I., & López Pita, A. (2009). Numerical simulation of embankment—structure transition design. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 223(4), 331-343. doi:10.1243/09544097jrrt234Gallego, I., Muñoz, J., Rivas, A., & Sánchez-Cambronero, S. (2011). Vertical Track Stiffness as a New Parameter Involved in Designing High-Speed Railway Infrastructure. Journal of Transportation Engineering, 137(12), 971-979. doi:10.1061/(asce)te.1943-5436.0000288Insa, R., Salvador, P., Inarejos, J., & Roda, A. (2011). Analysis of the influence of under sleeper pads on the railway vehicle/track dynamic interaction in transition zones. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 226(4), 409-420. doi:10.1177/0954409711430174Li, D., & Davis, D. (2005). Transition of Railroad Bridge Approaches. Journal of Geotechnical and Geoenvironmental Engineering, 131(11), 1392-1398. doi:10.1061/(asce)1090-0241(2005)131:11(1392)Pita, A. L., Teixeira, P. F., & Robuste, F. (2004). High speed and track deterioration: The role of vertical stiffness of the track. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 218(1), 31-40. doi:10.1243/095440904322804411Molatefi, H., & Izadbakhsh, S. (2013). Continous rail absorber design using decay rate calculation in FEM. Structural Engineering and Mechanics, 48(4), 455-466. doi:10.12989/sem.2013.48.4.455Montalbán, L., Real, J., & Real, T. (2012). Mechanical characterization of railway structures based on vertical stiffness analysis and railway substructure stress state. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 227(1), 74-85. doi:10.1177/0954409712452348Montalbán Domingo, L., Real Herraiz, J. I., Zamorano, C., & Real Herraiz, T. (2014). Design of a new high lateral resistance sleeper and performance comparison with conventional sleepers in a curved railway track by means of finite element models. Latin American Journal of Solids and Structures, 11(7), 1238-1250. doi:10.1590/s1679-78252014000700009Montalbán Domingo, L., Zamorano Martín, C., Palenzuela Avilés, C., & Real Herráiz, J. I. (2014). Analysis of the Influence of Cracked Sleepers under Static Loading on Ballasted Railway Tracks. The Scientific World Journal, 2014, 1-10. doi:10.1155/2014/363547Real, J. I., Gómez, L., Montalbán, L., & Real, T. (2012). Study of the influence of geometrical and mechanical parameters on ballasted railway tracks design. Journal of Mechanical Science and Technology, 26(9), 2837-2844. doi:10.1007/s12206-012-0734-7Shan, Y., Albers, B., & Savidis, S. A. (2013). Influence of different transition zones on the dynamic response of track–subgrade systems. Computers and Geotechnics, 48, 21-28. doi:10.1016/j.compgeo.2012.09.006Shi, J., Burrow, M. P. N., Chan, A. H., & Wang, Y. J. (2012). Measurements and simulation of the dynamic responses of a bridge–embankment transition zone below a heavy haul railway line. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 227(3), 254-268. doi:10.1177/095440971246097

Complex conductivity of soils

The complex conductivity of soils remains poorly known despite the growing importance of this method in hydrogeophysics. In order to fill this gap of knowledge, we investigate the complex conductivity of 71 soils samples (including four peat samples) and one clean sand in the frequency range 0.1 Hz to 45 kHz. The soil samples are saturated with six different NaCl brines with conductivities (0.031, 0.53, 1.15, 5.7, 14.7, and 22 S m21, NaCl, 258C) in order to determine their intrinsic formation factor and surface conductivity. This data set is used to test the predictions of the dynamic Stern polarization model of porous media in terms of relationship between the quadrature conductivity and the surface conductivity. We also investigate the relationship between the normalized chargeability (the difference of in-phase conductivity between two frequencies) and the quadrature conductivity at the geometric mean frequency. This data set confirms the relationships between the surface conductivity, the quadrature conductivity, and the normalized chargeability. The normalized chargeability depends linearly on the cation exchange capacity and specific surface area while the chargeability shows no dependence on these parameters. These new data and the dynamic Stern layer polarization model are observed to be mutually consistent. Traditionally, in hydrogeophysics, surface conductivity is neglected in the analysis of resistivity data. The relationships we have developed can be used in field conditions to avoid neglecting surface conductivity in the interpretation of DC resistivity tomograms. We also investigate the effects of temperature and saturation and, here again, the dynamic Stern layer predictions and the experimental observations are mutually consistent

FRACTAL ANALYSIS OF TRACK GEOMETRY DATA

An ongoing Federal Railroad Administration (FRA)-sponsored research project at the University of Massachusetts has been exploring the use of fractal analysis of track geometry data for indicating track geometry condition, planning maintenance, and evaluating the cause of substructure-related problems. Results indicate that fractal analysis is able to provide unique numerical values (fractal dimensions) that characterize railway track geometry patterns, can discern different orders or roughness within track geometry data, and is effective for maintenance management by providing independent fractal parameters for trend analysis and geometry deterioration assessment. Fractal theory is discussed, and the usefulness of fractal analysis for quantifying railroad geometry data is demonstrated by highlighting key aspects of the research results. The relationship between track structure conditions and fractal dimensions for use in maintenance planning and condition evaluation is also discussed