Effect of round particles on shear strength properties of railway ballast

Abstract

The railway industry in South Africa is facing a problem where passage of trains on the heavy coal haul lines are causing degradation by means of wear (roundness) of ballast materials, and consequently, leading to differential track settlement and unevenness of the surface. Railway ballast remains an important component material in a rail track structure system. However, their fundamental attributes of shape have not been determined accurately, and quantitatively related to the performance of the tracks in a more rigorous and scientific way. This paper presents a case study of five ballast materials used by Transnet Freight Rail heavy coal line in South Africa. The objective is to investigate the effect of ballast particle roundness determined from a modern three-dimensional (3-D) laser scanning technique on the internal frictional angle of the ballast materials. The results indicated the effect of ballast shape on shear strength, as fresh ballast from the quarry provided higher internal frictional angle when compared with ballast that have been degraded and rounded. It was established that there is a strong relationship between frictional angle and roundness (i.e. shape) of the ballast materials and a pebble sample that was used as a control material for extremely rounded ballast.