Ballast bed cleaning and recycling – influence on stability of continuously welded rail track

Abstract

The ballast bed main functions are to bind the sleepers to the substructure, to distribute the dynamic loads from the vehicle to the embankment and to ensure the track stability. Fouling may increase in time due to various reasons, under normal dynamic loads. If the ballast bed functions are no longer fulfilled, the welded track can lose its stability with highly damaging results. The purpose of the paper is to investigate the ballast bed fouling degree on welded tracks, with potential loss of stability. Once the ballast bed elasticity decreases and the geometry of the track cross section is modified, the track is subjected to longitudinal axial compression due to thermal loads that can result in stability lost: buckling of the rail. The ballast bed is required to ensure lateral and longitudinal resistance to the track. The lateral resistance force depends on the ballast depth, material properties, maintenance and tamping. The study uses the Energy Method to determine the critical stability force on fouled ballast bed conditions, with irregular settlements due to insufficient track maintenance. Continuously welded track stability was studied for three different fouling cases, both on curved track and on straight line, with various types of horizontal geometrical imperfections, using the maximal thermal effort as a reference. The results of the critical stability force determined using the Energy Method were compared to a real study case situation from a rail sector were ballast bed cleaning was performed. The paper aims to correlate the fouling degree of the ballast bed to continuously welded track stability problems due to thermal effect in connection with insufficient track maintenance. The critical stability force in three various situations were compared to the maximum temperature effort due to thermal load taking into consideration the geometrical aspect of the line, fouling degrees and existing geometrical imperfections.