Influence of aggregate degradation on the permeability of railway ballast

ABSTRACT

The main function of the railway structure is to provide stability and security so that rail transport operates efficiently. Its main constituents on the subgrade are ballast, sub-ballast, sleepers and rails. The ballast is an element of the superstructure that is located between the sleepers and the sub-ballast. The main functions of the ballast are the stress distribution and the contribution to the drainage of the structure. However, the impact caused by the passage of the trains cause the degradation of the aggregate and produces fines that damages to the drainage of the structure. Ineffective drainage can lead to the appearance of defects in the superstructure such as the displacement of the sleepers and the unevenness of the railroad due to the occurrence of permanent deformations in the geotechnical layers. In this context, the objective of this work was to evaluate the degradation of the ballast and the way in which this phenomenon influences its draining capacity. For this, in a first step, characterization tests of the material were carried out. The experimental method consisted of the accelerated degradation of basalt samples in the abrasion Los Angeles drum. Then, the permeability evaluation of the material was performed. It was possible to verify the relation between the phenomena of fouling and permeability from the clean ballast to the highly fouled ballast. It was evidenced that the 19.1 mm aggregate fraction suffered greater degradation, contributing to the fines increase in the system, being responsible for the fouling phenomenon, representing a harmful element in relation to the drainage of the rail ballast.

Keywords railway ballast; degradation of the aggregate; fouling; permeability of the ballast