Laboratory investigation and modelling of alternative materials for sub-ballast and formation rehabilitation in a heavy haul railway line

Abstract

The sub-ballast layer plays a key role in railway track performance, especially under heavy haul conditions such those of the Carajás Railway (EFC) – Brazil, where axle loads are expected to increase to 40 t/axle – a level achieved by few railways globally. Reusing ballast undercutting waste and soils is also critical, given the large volumes generated and the need for proper disposal when reuse is not feasible, in compliance with environmental regulations. This study explores the potential reuse of ballast undercutting waste and soils from the railway track region in sub-ballast applications for heavy-haul railway infrastructure. The goal is to define performance requirements for these alternative sub-ballast materials such as fine silty-sand and lateritic gravelly-sandy soils when compacted using the Rail-mounted Formation Rehabilitation Machine (RFRM) system, which performs multiple rehabilitation functions to meet design standards based on geotechnical parameters. The study includes laboratory testing and numerical modelling to support decision-making regarding the implementation of a RFRM system. Laboratory tests include physical, strength, deformability, compaction, and mechanical behaviour evaluations, some using a developed compaction quality evaluation box-test equipment. Numerical models, calibrated with experimental data, simulate various load, material, and moisture conditions under EFC-specific configurations. The findings concluded that RFRM compaction alone is insufficient for structural performance under 40 t/axle loads unless the formation soil is adequately improved and the previous conditions is guaranteed. The study showed that only lateritic gravelly-sandy soils with suitable geotechnical properties and recycled fouled ballast waste (RFBW) are compatible with RFRM compaction under 40 t/axle loads if treated with cement due to their favorable mineralogy which improved compaction and strength. The study supports the technical and environmental feasibility of reusing fouling ballast waste in sub-ballast layers and offers practical guidance for designing track rehabilitation solutions in heavy-haul contexts. It is recommended that different vibratory plate compaction configurations be analyzed further as well as the resilient and long-term behavior of the investigated materials.