INFLUENCE OF TRAIN AXLE LOAD ON MECHANICAL BEHAVIOR OF FOULED BALLAST

Abstract

This study evaluates the mechanical behavior of railway ballast under severe transient loading, using a laboratory drop weight impact test to simulate the effects of high-magnitude axle load events rather than direct axle loading. Crushed granite aggregates were subjected to standard characterization tests, including specific gravity, flakiness index, and elongation index, in accordance with AREMA specifications, confirming their suitability for railway applications. Ballast samples were prepared within a particle size range of 10–60 mm and tested in both clean and artificially fouled conditions at 10%, 30%, and 50% fouling levels using lateritic fines. A drop-weight impact test was conducted using a 19.2 kg hammer dropped from incremental heights of 200 mm to 1000 mm. Settlement, deformation ratio, resilient modulus and ballast breakage index (BBI) were measured to assess ballast performance under repeated loading. The results indicate a consistent decrease in resilient modulus and a corresponding increase in deformation ratio and BBI with increasing drop height and fouling level. Clean ballast exhibited superior stiffness and resistance to deformation, while heavily fouled ballast showed significant degradation in load-bearing capacity and elastic recovery. Quantitatively, the resilient modulus of 50% fouled ballast was 78% lower than that of clean ballast at a 200 mm drop height and BBI increased from 0.14 for clean ballast to 0.58 for 50% fouled ballast at 1000mm drop height. The findings establish an inverse relationship between resilient modulus and deformation ratio across all test conditions.