Influence of ballast shoulder width and track superelevation on the lateral resistance of a monoblock sleeper using discrete element method

Abstract

Railway tracks must resist lateral horizontal forces associated with curving and wind loading of trains and provide lateral restraint to prevent rail buckling in hot weather. On a ballasted railway, the required resistance is provided at the sleeper-ballast interface and is influenced by the shape and type of sleeper and the characteristics and profile of the ballast bed. In this study, numerical simulations of Single Tie Push Tests (STPTs) were carried out using the discrete element method (DEM) to investigate the effect of shoulder width and track superelevation on the lateral resistance of unloaded monoblock sleepers. Few previous studies of lateral resistance have considered the effect of superelevation, which is perhaps surprising as the horizontally-curved track is usually superelevated (canted) so that the downslope component of the train weight provides some of the centripetal force needed for the train to travel in a curved arc. It is found that the lateral resistance of a single sleeper increased with the degree of superelevation, by about 100% at 2 mm sleeper displacement for a superelevation of 150 mm compared with an uncanted sleeper. Most of this increase came from the shoulder ballast; the contribution from the crib increased slightly while that from the base reduced slightly. Widening the ballast shoulder from 300 to 500 mm resulted in an increase in resistance of about 27% regardless of the superelevation. The results indicate the importance of maintaining the ballast shoulder, especially in superelevated track sections.