Towards real-time condition monitoring of a transition zone in a railway structure using fibre Bragg grating sensors

Abstract

Differential settlement of ballast and subgrade is a common issue in ballasted railway tracks. In transition zones between two different track forms, such as between a ballasted track and a slab track, a dip in longitudinal level often develops on the ballasted side. To ensure the safety of railway operation and reduce maintenance and life cycle costs, it is necessary to monitor the condition of the transition zone in an economical manner and to detect any operational change at an early stage. In recent years with the advancement of fibre-optic technology, fibre Bragg grating (FBG) sensors have been more commonly applied in condition monitoring of railways due to their high precision and high acquisition rates. In this study, an FBG-based setup for in-situ long-term condition monitoring of track bed degradation in a transition zone has been developed and implemented to provide data for verification and calibration of a simulation model. The system is designed for measurements in an operational railway track in harsh conditions in the north of Sweden. The instrumentation along the transition includes four clusters, each with an optical strain gauge array on the rail web in one sleeper bay, and an accelerometer and a displacement transducer on the sleeper. It is shown that the implemented displacement and strain sensors are able to effectively capture the overall dynamic range of the system, indicating that the collected data can accurately represent the dynamic response of the transition zone in the short term and long term and be applied for the calibration of a simulation model.