Monitoring Railway Infrastructure in Norway using Geophysics and Distributed Acoustic Sensing: The Bolstadstrandi Case Study

The study discusses the potential application of investigating subsurface structures using active and passive geophysical methods along the railway in Norway. The primary goal is to track groundwater level fluctuations and correlate them with hazard events near the rail track. The test site is located in Western Norway, where significant precipitation and extreme weather events often cause structural failures along the railway infrastructure. Active methods, including Ground Penetrating Radar (GPR) surveys, were conducted repeatedly along several profiles, while seismic surveys using Multichannel Analysis of Surface Waves (MASW) provided preliminary 1-D shear-wave velocity (Vs) profiles as a reference for passive analysis. The passive seismic methods, including DAS along dark fibre and three-component geophones, were employed to analyze ambient noise and extract surface waves. Geotechnical sounding was previously performed, and continuous monitoring of groundwater levels and soil moisture using sensors was deployed to validate the DAS and geophysical measurements. Initial analyses demonstrate the potential for subsurface monitoring using time-lapse methods like coda-wave interferometry and ambient-noise interferometry. Future studies will focus on expanding the dataset, refining velocity models, and enhancing calibration with ground-truth data.