Remote sensing of track degradation using InSAR – a case study of the Iron ore line

Track irregularities induce increased wheel-rail contact forces causing poor ride comfort, accelerated mechanical degradation of vehicle and track or even failures that may lead to speed restrictions or temporary track closure. Today’s monitoring of railway tracks in Sweden using measurement vehicles consumes traffic capacity and means a restriction in data collection to a few occasions per year. Remote sensing such as Interferometric Synthetic Aperture Radar (InSAR) can be used to monitor ground deformation in the close vicinity of the track with potential impact on the track substructure. The importance of geotechnical properties of the track substructure on the development of track irregularities is well known from experience and literature and is demonstrated for example by the re-development of discrete track irregularities at the same locations after tamping. The Sentinel 1A and 1B satellites have collected data every 12th day resulting in roughly weekly observations between 2016 and 2021. This case study evaluates the relationship between ground deformation in the ascending and descending tracks, basic geological properties and track irregularity. The average negative ground movement rate measured using InSAR was higher for track segments that had experienced poor track geometry in the ascending path, especially for track built on clay, moraine or glaciofuvial deposits. A higher variance in ground motion was found in both the ascending and descending path near segments which had experienced track geometry alerts. Future work should further investigate these relationships by observing vertical and horizontal movement separately, incorporating a temporal dimension, and increasing spatial resolution, taking special consideration to variation of settlement surrounding and along the track.