Performance Evaluation of Nigeria Railway Track Ballast Under Simulated Operational Conditions

Over time, most research on railway track performance has focused mainly on rail and track geometry, with a few considering the damage or degradation occurring at the substructure level. This paper presents a step-by-step comprehensive study on the performance evaluation of selected uncontaminated ballast under simulated operational conditions and contaminated ballast (i.e., fouled) based on a series of laboratory tests. Tested parameters included granulometry, strength, durability and drainability and were compared with the recognised railway ballast requirements. The topsoil used as one of the fouling agents is classified into the ML group as inorganic silt with median compressibility. The initial gradation of the ballast indicates that the clean ballast samples are typically uniformly graded and generally strong and suitable for use following relevant recommendations. The abrasion tolerance of the uncontaminated ballast samples from both test locations increased as the cyclic/repeated loading induced by the train increased. The ballast gradation curves for each mix after the fouling process in the worst case of degradation by abrasion and contaminant shifted to broad-graded classification due to the presence of finer-sized particles. Generally, the higher the content of the fouling agent as ballast contamination, the lower the hydraulic conductivity. However, the inclusion of diesel as liquid intrusion does not seem to have any significant effect on the hydraulic conductivity. The study further presents an empirical model capable of predicting the hydraulic conductivity of ballast. The study concluded with admissible ballast contamination for cleaning and maintenance works.