InSAR supported by geophysical and geotechnical information constrains two-dimensional motion of a railway embankment constructed on peat

Abstract

Rail and road embankments constructed on peatlands are subjected to significant challenges due to the high compressibility of peat. They are, therefore, susceptible to considerable settlement following construction. Accurate and timely monitoring of such embankments is important in order to enable proactive intervention strategies and to avoid failures. Multi-temporal Synthetic Aperture RADAR Interferometry (MT-InSAR) techniques applied to satellite-derived SAR data have been shown to be effective for remotely measuring and monitoring the deformation of civil engineering infrastructure. This paper presents a comprehensive approach, involving MT-InSAR supported by local geophysical and geotechnical information, for the detection and investigation of the movement of a railway embankment constructed on peatland. The Small Baselines approach, implemented in StaMPS (referred to as StaMPS-SB), was performed to measure long-term deformation of the embankment in vertical, horizontal east-west and satellite line-of-sight (LOS) directions. In this regard, a Sentinel-1 A/1B dataset composed of 362 descending images, acquired from 2015 to 2022, was analysed to measure LOS displacement. Also, 282 Sentinel-1 A/1B images of both ascending and descending tracks, collected from 2017 to 2022, were analysed to obtain vertical, horizontal and LOS displacements. According to the results, the maximum ground motion rate along the LOS direction was −29 mm/year for the period from 2015 to 2022. However, from 2017 to 2022, this value was about −25 mm/year and − 22 mm/year for descending and ascending tracks, respectively. During this period, the maximum motion rate obtained was −23.1 mm/year in the vertical direction. Moreover, horizontal movement up to −10 mm/year was observed in the westward direction and + 7 mm/year in the eastern direction. We used in-situ data to support corroborate and improve our interpretation of the InSAR results. In this context, peat thickness profiles, records of tamping activities and interpretations of the railway ballast base from ground penetrating radar data, were employed. The in-situ data revealed that the embankment section exhibiting the greatest vertical motion detected by InSAR corresponds closely to the thickest section of railway ballast, the zone of greatest number of tamping activities and the deepest section of peat. As such, this case study highlights how remote detection of embankment motion, coupled with targeted in-situ investigation, can underpin proactive intervention to improve safety.