Heavy Haul Railroad Design Upgrading Based on Fundamental Track Dynamics

Tucho, Ameyu Temesgen

Heavy Haul Railroad Design Upgrading Based on Fundamental Track Dynamics

Tucho, Ameyu Temesgen

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Publication Type:: Thesis
Issue Date:: 2023

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Field	Value	Language
dc.contributor.author	Tucho, Ameyu Temesgen
dc.date.accessioned	2023-10-17T00:16:03Z
dc.date.available	2023-10-17T00:16:03Z
dc.date.issued	2023
dc.identifier.uri	http://hdl.handle.net/10453/172712
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	Railways have become one of the most preferred passenger and freight transportation modes in many countries. The past decades have witnessed a significant increase in demand for higher performance from the existing and new rail networks to retain a competitive edge against other transportation systems. This has motivated the railway industry to seek faster, heavier trains while satisfying performance requirements. High-speed and heavy axle loads pose various geodynamic and geotechnical challenges in ballasted tracks. The major challenge at elevated train speed is excessive ground vibration and stress amplification, mainly when the speed is close to the critical wave velocity of the track. Those elevated vibrations increase safety issues since large track displacement can cause a derailment, whereas stress amplification could result in excessive deformation and track instability. In this study, a three-dimensional (3D) finite element (FE) analysis is developed to study the effect of moving load on the dynamic response of rail tracks. The FEM model is validated with two different field measurements, which are used to study the effect of train speed on the transient stress-displacement response of ballasted track. Increasing train speed amplifies vertical and lateral track displacement and alters the displacement field, especially at a critical speed. Also, the critical speed and magnitude of track deflection are observed to be influenced by subgrade modulus. The changes attributed to dynamic stress paths and the angle of principal stress rotation are also analysed for the train speed in the range of 60-450 km/h. The conventional approach predicting track stress does not capture track response involving moving load and associated “critical speed” effect, especially at higher speeds where significant principal stress reversal occurs. Also, the analysis shows the existence of maximum allowable train speed to prevent shear failure of the ballast layer. After the effect of speed on track vibration and associated amplification of stress-displacement field is established through 3D FE analysis, the potential application of rubber inclusion in the ballast layer was examined. In this study, the traditional ballast layer was replaced by a Rubber-Intermixed-Ballast system (RIBS), and the response of the track under moving train loading is studied. The analysis was conducted at various train speeds to capture the distinct track response at pseudo-static, subcritical, and critical speed ranges. Finally, the practical implication of RIBS on global track response is analysed and discussed in terms of vertical stress reduction and transient displacement in the vertical and lateral directions.	en_US.UTF-8
dc.format	Thesis (PhD)
dc.language.iso	en_US	en_US.UTF-8
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/172712/1/thesis.pdf
dc.rights	info:eu-repo/semantics/embargoedAccess
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	© 2023 Ameyu Temesgen Tucho
dc.rights	au.edu.uts.lib/cph
dc.title	Heavy Haul Railroad Design Upgrading Based on Fundamental Track Dynamics	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*
utslib.copyright.embargo	2024-07-28T00:00:00+1000

Abstract:

Railways have become one of the most preferred passenger and freight transportation modes in many countries. The past decades have witnessed a significant increase in demand for higher performance from the existing and new rail networks to retain a competitive edge against other transportation systems. This has motivated the railway industry to seek faster, heavier trains while satisfying performance requirements. High-speed and heavy axle loads pose various geodynamic and geotechnical challenges in ballasted tracks. The major challenge at elevated train speed is excessive ground vibration and stress amplification, mainly when the speed is close to the critical wave velocity of the track. Those elevated vibrations increase safety issues since large track displacement can cause a derailment, whereas stress amplification could result in excessive deformation and track instability. In this study, a three-dimensional (3D) finite element (FE) analysis is developed to study the effect of moving load on the dynamic response of rail tracks. The FEM model is validated with two different field measurements, which are used to study the effect of train speed on the transient stress-displacement response of ballasted track. Increasing train speed amplifies vertical and lateral track displacement and alters the displacement field, especially at a critical speed. Also, the critical speed and magnitude of track deflection are observed to be influenced by subgrade modulus. The changes attributed to dynamic stress paths and the angle of principal stress rotation are also analysed for the train speed in the range of 60-450 km/h. The conventional approach predicting track stress does not capture track response involving moving load and associated “critical speed” effect, especially at higher speeds where significant principal stress reversal occurs. Also, the analysis shows the existence of maximum allowable train speed to prevent shear failure of the ballast layer. After the effect of speed on track vibration and associated amplification of stress-displacement field is established through 3D FE analysis, the potential application of rubber inclusion in the ballast layer was examined. In this study, the traditional ballast layer was replaced by a Rubber-Intermixed-Ballast system (RIBS), and the response of the track under moving train loading is studied. The analysis was conducted at various train speeds to capture the distinct track response at pseudo-static, subcritical, and critical speed ranges. Finally, the practical implication of RIBS on global track response is analysed and discussed in terms of vertical stress reduction and transient displacement in the vertical and lateral directions.

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