The Effect of Confining Pressure on the Behaviour of Railway Ballast Under Cyclic Loading

During train loading, the railway substructure is subjected to loading amplitudes that can, over time, cause serious track alignment and stability problems. Railway substructure problems have become more serious and widespread in recent years due to the employment of faster and heavier trains. Railway authorities throughout Australia are faced with shortening maintenance cycles, and substantial increases in maintenance costs. With train speeds, loads and frequency expected to continue to increase, finding new and innovative ways to strengthen the substructure, in particular the ballast layer, is vital for the continued safe and economical use of both passenger and freight trains. This project investigates three possible ways in which the substructure can be strengthened; by a) altering the magnitude of confining pressure on the load bearing ballast, b) optimising the ballast particle size distribution, and c) employing the use of geosynthetics within the substructure as a form of reinforcement. In this paper, a large-scale triaxial apparatus is used to examine the effect of confining pressure on the degradation and settlement characteristics of ballast. It was found that increasi ng the confining pressure leads to a significant reduction in settlement but increased ballast breakage.