A review of methods and challenges for monitoring of differential settlement in railway transition zones

Paper in proceeding, 2025

Differential settlement in ballasted railway tracks, particularly in transition zones between two track forms, poses a critical challenge for railway infrastructure. Such settlement, often exacerbated by a stiffness gradient due to changes in track superstructure and substructure, typically causes a local dip in the longitudinal track level a few metres from the transition, leading to higher dynamic traffic loading and reduced passenger comfort. Regular monitoring of transition zones is essential for safe operations and cost-effective maintenance. This paper reviews methods for monitoring differential settlement in railway tracks. To measure the properties and loading of the superstructure, potential methods include fibre Bragg grating (FBG) sensors, point receptance measurements, track geometry (and track stiffness) recording cars, and wheel load impact detectors (WILD). Characterisation of the subgrade can be carried out via a multichannel analysis of surface waves (MASW), dynamic cone penetration tests (CPT), interferometric synthetic aperture radar (InSAR), frost sticks for temperature monitoring, and total stations. Lessons learned from an in-situ measurement involving an extensive FBG-based system deployed in northern Sweden to monitor a transition zone in harsh weather conditions are presented. Integrating a combination of monitoring methods with a simulation model to verify and support the accurate prediction of differential settlement is a useful approach to addressing challenges associated with track stiffness gradients and guiding the improvement of transition zone designs.