Effect of clay fouling on track drainage capacity of railway Ballast: Experimental and numerical study

Abstract

Ballast fouling is a key contributor to the instability of ballasted railway tracks due to its detrimental influence on the permeability of the ballast layer. Predicting the track drainage condition in a ballasted track segment frequently affected by fouling is vital for planning track maintenance activities. However, only limited studies have been conducted to assess the hydraulic conductivity and track drainage capacity of fouled railway ballast. Hence, full-scale permeability tests were performed in this study using an in-house custom-built large-scale permeability apparatus at the laboratory to attain hydraulic conductivities for 5 different fouling levels of ballast fouled with sandy lean clay material. Based on the experimental results, a relationship between the Void Contamination Index (VCI) and hydraulic conductivity was obtained. The results elucidated that the fouling material reduced the hydraulic conductivity of ballast by more than 90% when VCI was 25% or higher. In addition, using the hydraulic conductivity values obtained from experimental results, a detailed 2D numerical seepage analysis of a rail track was carried out to represent the track drainage capacity at various fouling levels. Based on the results, the significance of maintaining a clean top ballast layer and shoulder ballast was highlighted and a criterion for estimating the drainage capacity of a clay-fouled railway track was proposed to initiate track maintenance operations.