Mechanical properties of re-used ballast

Abstract

There is an urgent need to decarbonise transport– this includes the infrastructure. Railways have a key role to play in decarbonising transport because they are very energy-efficient, but the infrastructure and its upkeep are costly in money and carbon. Infrastructure maintenance requirements are likely to increase if the number, speed and weight of trains increase. This makes reducing the maintenance needs of the railways even more urgent. Traditionally, ballast has been considered to be life-expired after 10-50 tamps – typically about 30 years of service on moderate to busy lines. Overall maintenance needs could be reduced by reducing the need to maintain and then to replace ballast. This can be achieved by better understanding the performance of used ballast – cleaned and recovered. This thesis presents quantitative research into the relative shape properties of fresh and used ballast and relates these quantitative measures of shape to tested performance. Methods of evaluating surface roughness for railway ballast are proposed. Shape characterisation showed no significant difference in form between fresh and used ballast, a slight reduction in angularity in used ballast, and a significant reduction in roughness in used ballast. Scaled used ballast was synthesised for triaxial shear testing in the laboratory by abrading scaled fresh ballast in the Micro-Deval apparatus to a target shape equal to that of the used ballast. Effects of surface roughness and grain attrition due to loading on frictional properties of ballast were also investigated. Fresh and used ballast showed similar contact frictional properties. The study found that although the roughness of used ballast was smaller than that of fresh, both were similar in shape and showed similar strength properties. Ballast developed a stable structure over a few hundred thousand loading cycles. The resilient modulus increased by up to 60% with an increase in load cycles until about 200000 cycles; after this point, there was no significant increment. Cyclic loading improved the ballast strength by up to 15%. The study found that life-expired ballast of granitic origin could be reused.

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Identifiers

ORCID for Antonios Zervos: orcid.org/0000-0002-2662-9320

ORCID for Louis Le Pen: orcid.org/0000-0002-4362-3895

ORCID for Madhusudhan Bangalore Narasimha Murthy: orcid.org/0000-0002-2570-5934

ORCID for William Powrie: orcid.org/0000-0002-2271-0826

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