Strength Properties and Behavior of Fresh and Abraded Railway Ballasts in Unsaturated Conditions

Abstract

Railway ballast is an important component of the railroad substructure, providing resistance to forces, distribution of loads to reduce stress on the subgrade, and drainage of water away from the track. To better understand the strength properties and behavior that govern its ability to perform these tasks, laboratory testing can be performed on ballast under various conditions. In this study, 10-inch (25.4 cm) diameter triaxial specimens are prepared using an abraded ballast most closely matching AREMA #4 gradation, taken from track located in Shelburne Falls, Massachusetts. Each specimen is prepared to the same density, with variation in water content and confining pressures tested. Tests are performed in the dry condition, field capacity condition, and at 50% of field capacity. For each of these water contents, confining pressures of 5 psi (34.5 kPa), 10 psi (68.9 kPa), and 15 psi (103.4 kPa) are used. From these tests, friction angle, Poisson’s ratio, and Modulus of Elasticity are determined, as well as stress-strain and volumetric strain behavior. Furthermore, these results are compared to tests performed previously at the University of Massachusetts Amherst. This series of tests were performed under the same exact conditions, but instead used a highly angular, freshly quarried Connecticut granite. Comparison of these two materials under the same conditions provides an understanding of how ballast behavior and strength properties may change over time.