Deformation and degradation of railroad granular layers under high frequency cyclic loading and the benefits of using geosynthetics
The granular media (i.e., ballast and sub-ballast) used in ballasted rail tracks undergo large deformations along with particle breakage when subjected to cyclic loads exerted by heavy and fast trains. The deformation and degradation of such granular layers severely affects track geometry and results into increased maintenance costs. The use of artificial inclusions in planar (geogrid, geotextile, and geocomposite) as well as three-dimensional form (geocell) is essential to curtail such costs and improve track stability. A series of cyclic drained triaxial tests were conducted using large-scale prismoidal process simulation apparatus designed and built at the University of Wollongong. Effects of external confining pressure, frequency, and number of load cycles were investigated. The test results showed that large deformation and degradation of ballast was imminent under high frequency cyclic loading. It was also shown that settlement of the ballast and sub-ballast can be reduced significantly employing geocomposites and geocells, respectively. The results revealed the effectiveness of the geocell, when they are used at low confinement and higher frequencies. This paper provides an insight to cyclic behavior of railroad granular substructure and demonstrates the role of confinement induced through the use of artificial inclusions.