Fouling conditions and associated deformation characteristics of railway ballast

Ballast is an essential component of the railway track substructure to facilitate load distribution and drainage. However, during service life, ballast loses its strength by reducing friction properties and gets fouled, which fails to perform as desired. Therefore, highly fouled ballast needs to be either cleaned or replaced to restore the expected load-bearing capacity, resiliency, track geometry, and drainage properties. Therefore, it is important to identify the intensity of ballast fouling and the characteristics of fouling materials along with their effect on the strength and deformation of the railway ballast. In this study, field investigation includes a collection of ballast samples from the live railway track of Bangladesh, and related tests are conducted. Based on the findings of the field identification, ballast samples on a scale of 1/5th are prepared in the laboratory with desired gradation and material properties to replicate the field samples. Compaction tests and a series of consolidated drained cyclic triaxial tests are conducted to identify the strength and deformation characteristics of the fouled ballast, considering the effect of water content. Based on the fouling index, four out of six samples are highly fouled, and the fouling materials contain both plastic and non-plastic properties. Triaxial test results indicate that consistency of the fouling material, degree of saturation, and deviator stress level significantly affect the strength and deformation characteristics of the fouled railway ballast. Fouling materials containing plastic properties increases the risk to the stability of the railway track in the presence of moisture.