Experimental and Numerical Study of Rubber Intermixed Ballast System Subjected to Monotonic and Cyclic Loading

Kulappu Arachchige, Chathuri Madhusanka

Experimental and Numerical Study of Rubber Intermixed Ballast System Subjected to Monotonic and Cyclic Loading

Kulappu Arachchige, Chathuri Madhusanka

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Publication Type:: Thesis
Issue Date:: 2022

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Field	Value	Language
dc.contributor.author	Kulappu Arachchige, Chathuri Madhusanka
dc.date.accessioned	2023-01-13T02:33:44Z
dc.date.available	2023-01-13T02:33:44Z
dc.date.issued	2022
dc.identifier.uri	http://hdl.handle.net/10453/164951
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	Quarried natural rock aggregates are the most demanded type of railway ballast worldwide, attributed to their favourable physical, geotechnical and mechanical properties. After a certain period of operation and fatigue under repeated loading, degraded ballast requires replenishment with freshly quarried ballast, which is one of the most expensive items in track maintenance schemes. Given the current environmental issues, as well as the challenges in obtaining very large quantities of ballast, railway authorities have now looked for other alternatives. This doctoral study promotes the concept of using rubber granules from waste tyres as elastic aggregates appropriately blended with traditional ballast aggregates for enhanced performance of rail tracks, i.e., a Rubber Intermixed Ballast Stratum (RIBS). During the course of this study, large-scale laboratory experiments were conducted to examine the geotechnical characteristics of RIBS under monotonic loads, and an acceptance criterion was established to determine the rubber content required to optimise the performance. The outcomes demonstrate that the proximity of 10% rubber granules by weight in the blended assembly, can significantly reduce dilation, control the degradation of the deformation modulus as well as reduce the breakage of natural rock aggregates. However, much higher rubber contents (>15%) may overly reduce the shear strength of the granular mix and also induce relatively large initial settlements. More significantly, replacing the ballast size fraction with rubber particles ranging from 9.5 to 19 mm with similar angularity is certainly advantageous as they also reduce the breakage of load-bearing coarse aggregates, thus effectively controlling ballast fouling. The study was further extended to evaluate the characteristics of RIBS subjected to typical cyclic loads by conducting large-scale triaxial tests following a monotonic conditioning phase. The results indicate that irreversible rearrangement of grain configurations during the conditioning phase was pronounced in RIBS leading to a reduction in deformation during cyclic loading. It was also demonstrated that RIBS increases the energy absorption capacity and damping properties compared to fresh ballast, and reduces ballast breakage while maintaining an adequate resilient modulus. Moreover, a constitutive model for rubber-mixed ballast has been developed to explain fundamentally the stress-dilatancy behaviour of RIBS. In a practical perspective, the application of RIBS in real-life tracks is elucidated to encourage railway asset owners and R&D stakeholders to adopt and implement RIBS given its proven sound geotechnical and mechanical properties. Finally, salient considerations of track design and construction are discussed in relation to the use of RIBS while recognising its limitations.	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/10453/164951/2/02whole.pdf
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	info:eu-repo/semantics/openAccess
dc.rights	au.edu.uts.lib/ppc
dc.title	Experimental and Numerical Study of Rubber Intermixed Ballast System Subjected to Monotonic and Cyclic Loading	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

Quarried natural rock aggregates are the most demanded type of railway ballast worldwide, attributed to their favourable physical, geotechnical and mechanical properties. After a certain period of operation and fatigue under repeated loading, degraded ballast requires replenishment with freshly quarried ballast, which is one of the most expensive items in track maintenance schemes. Given the current environmental issues, as well as the challenges in obtaining very large quantities of ballast, railway authorities have now looked for other alternatives. This doctoral study promotes the concept of using rubber granules from waste tyres as elastic aggregates appropriately blended with traditional ballast aggregates for enhanced performance of rail tracks, i.e., a Rubber Intermixed Ballast Stratum (RIBS). During the course of this study, large-scale laboratory experiments were conducted to examine the geotechnical characteristics of RIBS under monotonic loads, and an acceptance criterion was established to determine the rubber content required to optimise the performance. The outcomes demonstrate that the proximity of 10% rubber granules by weight in the blended assembly, can significantly reduce dilation, control the degradation of the deformation modulus as well as reduce the breakage of natural rock aggregates. However, much higher rubber contents (>15%) may overly reduce the shear strength of the granular mix and also induce relatively large initial settlements. More significantly, replacing the ballast size fraction with rubber particles ranging from 9.5 to 19 mm with similar angularity is certainly advantageous as they also reduce the breakage of load-bearing coarse aggregates, thus effectively controlling ballast fouling. The study was further extended to evaluate the characteristics of RIBS subjected to typical cyclic loads by conducting large-scale triaxial tests following a monotonic conditioning phase. The results indicate that irreversible rearrangement of grain configurations during the conditioning phase was pronounced in RIBS leading to a reduction in deformation during cyclic loading. It was also demonstrated that RIBS increases the energy absorption capacity and damping properties compared to fresh ballast, and reduces ballast breakage while maintaining an adequate resilient modulus. Moreover, a constitutive model for rubber-mixed ballast has been developed to explain fundamentally the stress-dilatancy behaviour of RIBS. In a practical perspective, the application of RIBS in real-life tracks is elucidated to encourage railway asset owners and R&D stakeholders to adopt and implement RIBS given its proven sound geotechnical and mechanical properties. Finally, salient considerations of track design and construction are discussed in relation to the use of RIBS while recognising its limitations.

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