Mechanical behavior of limestone ballast for heavy haul Brazilian railway lines: Laboratory evaluation

Abstract

Railway ballast is the granular material that supports the sleepers on a conventional railway track and whose mechanical behavior determines the performance and safety conditions of the track. The particles that make up ballast are generally derived from igneous or metamorphic rocks, particularly granite, basalt, gneiss, dolomite, rhyolite, and quartzite. Sedimentary rocks such as limestone are sometimes used but are not recommended. The purpose of this research is to evaluate the mechanical behavior of limestone ballast, specifically its shear strength, permanent deformation and particle breakage, with a view to determining its suitability for use in Brazilian heavy haul railway lines. This paper presents an experimental investigation of limestone aggregate through of monotonic and cyclic triaxial tests performed on full-scale ballast specimens. The monotonic triaxial tests were carried out at three different confining pressures to failure and to critical state, while the long-term cyclic tests (permanent deformation) were carried out in six stress paths compatible with real heavy haul loads, as well as milder and more severe stress levels. The results indicate that the limestone aggregate, despite the high proportion of non-cubic particles, can be satisfactorily used as a ballast material due to the high values of the strength parameters and the long-term deformability behavior, characterized by lower degradation and particle breakage and the tendency to stabilize the permanent deformation when the stress paths compatible with real-life heavy haul loadings were applied.