The structural performance of ballasted railway tracks is adversely affected by the level of degradation of the ballast particles. The aggregate particles of the ballast bed undergo gradual degradation which results to an axial deformation of the railway track during the service operation. However, the study of ballast degradation has been very complex and to date, there has not been a single method that is universally accepted to quantify ballast degradation. Hence, in an attempt to adequately quantify the degradation of ballast, this study compares the two most common methods used for the evaluation of ballast degradation; Fouling index (FI) and Marsal’s index (Bg). The degraded ballast material was prepared in the laboratory using the Los Angeles abrasion (LAA) method. The Los Angeles abrasion (LAA) test was conducted eight (8) times continuously on the same sample at an interval of 250 turns of the LAA test drum. A Series of sieve analysis was conducted after each test run and the changes in ballast gradations were evaluated. Based on the results obtained a strong correlation was observed between the two approaches with a coefficient of determination of 99.24%. Hence, both Marsal’s breakage index and the fouling index can be used for the evaluation of ballast degradation. However, Marsal’s breakage index is recommended due to its ability to give the breakdown of the particle size variations.

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Dr. Adamu Lawan