Effects of natural abrasion on railroad ballast strength and deformation properties

• Published in: Construction & building materials Vol. 247; p. 118315
• Main Authors: Rohrman, Andrew K., Kashani, Hamed F., Ho, Carlton L.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 30.06.2020
• Subjects: Abrasion; Ballast; Box test; Fouling; Triaxial test; Abrasion; Fouling; Triaxial test; Performance; Ballast; Box test
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2020.118315

Railway ballast is an important component of the track substructure that provides vertical, lateral, and longitudinal support, increases track resiliency, reduces stress applied to the subgrade, and facilitates the drainage of water away from the track. Ballast is typically composed of highly angular, uniformly graded crushed stone that provides high shear strength. However, the properties of ballast are continually changing under repeated loading from train traffic. Abrasion between ballast pieces often results in more rounded particles as corners are broken off. This process also contributes to fouling, or the introduction of finer grained particles into the ballast. Abraded material accounts for the majority of fouling, but it can also be introduced via other processes, such as infiltration from the subgrade or infiltration by windblown particles. While laboratory testing of ballast has been performed extensively over the past several decades, much of the testing is performed on fresh ballast with manufactured fouling materials. This study performs laboratory tests on naturally abraded ballast, taken from real track, and the naturally occurring fouling material which includes abraded and windblown material. This study builds on tests previously performed at the University of Massachusetts, Amherst which used fresh, highly angular ballast and fouling which originates from the same parent rock. Triaxial and box tests are performed on specimens, which are prepared to the same fouling and water contents as the previous testing so that the material properties and behaviors can be directly compared. The triaxial tests reveal similar strength properties, but significantly different volumetric strain behaviors. The box tests show similar results, with higher overall settlements from the abraded ballast, particularly under initial loading. This testing has also resulted in the first known basal failure of ballast in a box test. The results show that abraded ballast exhibits distinct behavioral differences, as well as reductions in performance when compared to highly angular ballast in the same conditions.