The Lee Tunnel was constructed as the first part of the Thames Tideway Improvement scheme, between 2010 and 2016. With tunnelling for the East section of the main Thames Tideway Tunnel, which joins the Lee Tunnel at Abbey Mills Pumping Station, beginning in early 2020, this paper investigates patterns of deformation in East London during construction of the Lee Tunnel. An unexpected geological feature, later identified as a drift filled hollow, was discovered during tunnelling. This study demonstrates that had eight years of ERS Persistent Scatterer Interferometry (PSI) data been analysed prior to tunnelling, the unusual pattern of displacement may have been recognised and further targeted borehole investigations taken place before the launch of the tunnel boring machine. Results also show how areas of different land use, including cemeteries and historic landfill, exhibit differences in settlement behaviour, compared with surrounding terraced housing. This research highlights the challenges in interpreting PSI results in an urban area with ongoing construction and the value of a long archive of data, which now spans almost three decades in London, that can be used to establish a baseline prior to construction.

London Clay, which underlies the majority of Greater London, has a high shrink–swell potential that can result in damage to foundations and surface infrastructure due to seasonal expansion and contraction of the clay. Currently, surface movement as a result of shrink–swell is not monitored in London, meaning that the magnitude and cyclicity of these movements is poorly understood. Persistent Scatterer Interferometric (PSI) Synthetic Aperture Radar data provide high-precision line-of-sight displacement measurements at a high point density across urban areas, offering the possibility of routine shrink–swell monitoring across whole cities. To test this, PSI data derived from TerraSAR-X (TSX) observations for the period from May 2011 to April 2017 were analysed for shrink–swell patterns across three areas of London in Hammersmith, Muswell Hill and Islington. A consistent cyclicity and amplitude was detected at all sites and the number of cycles is comparable with those identified in rainfall data. The amplitude of these cycles is smaller than anticipated, most probably because of the resisting effect of roads and pavements. The Cranfield University Leakage Assessment from Corrosivity and Shrinkage (LEACS) database was used to subdivide the PSI data and the average velocity and amplitude of each class statistically tested for significant differences between classes. The results show that it is not possible to statistically isolate possible soil shrink–swell movement in TSX PSI data in London. Thematic collection: This article is part of the Measurement and monitoring collection available at: https://www.lyellcollection.org/cc/measurement-and-monitoring

Analysis of ground movement rates along the coastline and upper sections of the Ventnor landslide complex was carried out utilizing Persistent Scatterer Interferometric Synthetic Aperture Radar methods using Sentinel-1 SAR data from 2015 to 2019 (four years). Results were compared with rainfall data, historical ground investigation records and monitoring surveys carried out at Ventnor to relate observations to geology, geomorphology and rainfall. Decomposition of InSAR viewing geometries to vertical and horizontal aligned well with previous ground-based studies. Subsidence of −9.8 mm a⁻¹ at the Lowtherville Graben and heave of +8.5 mm a⁻¹ along the coastline south of Ventnor Park were observed. Decomposition to east-west geometry results showed an eastward displacement of approximately 12.4 mm a⁻¹ along the coastline south of Ventnor Park, and a westward displacement of −3.7 mm a⁻¹ throughout built up sections of Ventnor town, indicating the landslide was displacing more in an eastern direction than vertically. The cause of this movement was investigated by using publicly available intrusive boreholes paired with Persistent Scatterer Interferometry, and a new ground model spanning east-west parallel to the coastline was presented. No evidence of significant ground movement was observed along heavily protected sections of the coastline, suggesting coastal defences comprised of concrete aprons and rip rap appear to be an effective coastal management/landslide stabilisation tool when compared to rip rap alone. The mechanism of this increased stability is likely due to the combination of toe weighting and reduced toe erosion. A lag of approximately 13–20 days was observed between high rainfall events and subsequent peaks in ground displacement, which was shorter than a 29 day lag observed in a previous study. Similar observations of prolonged rainfall resulting in prolonged displacements were also observed. The study demonstrates the capabilities of the PSI methodology in identifying the same ground movements that conventional methods provide. By providing detailed analysis of ground deformation of the Ventnor landslide, we demonstrate small ground movements, validated with existing ground movement surveys. Similar methodology can be applied to coastal landslides in urban environments worldwide, providing a relatively cheap and rapid resource for coastal landslide monitoring.

The benefits of InSAR to the civil engineering industry have been demonstrated on many occasions, however there is still a limited uptake by end-users, due to perceived differences between data providers and uncertainty around how to interpret results. This paper critically compares three datasets for London: Radarsat-2 (RS2) from 2011 to 2015, TerraSAR-X (TSX) from 2011 to 2017, and Sentinel-1 (STL1) from 2015 to 2017. Two of the datasets (TSX & RS2) were processed by commercial data providers, while the STL1 data were processed using ENVI ^® SARscape ^® by the authors. The results show an inverse relationship between the Pearson Correlation Coefficient and absolute total displacement of Persistent Scatterers (PS). There is a strong correlation between datasets for total displacement greater than 5 mm, but a weak or no correlation in the 0–3 mm range. Consequently, standard commercial InSAR datasets, processed with no a priori knowledge of the area of interest, have error margins below 3–5 mm but correctly detect all deformation phenomena exceeding this threshold. RS2-TSX both capture the spatial extent of the investigated area of dewatering induced subsidence, however STL1 measures a much broader, less pronounced zone of heave than TSX. Thematic collection: This article is part of the Remote sensing for site investigations on Earth and other planets collection available at: https://www.lyellcollection.org/cc/remote-sensing-for-site-investigations-on-earth-and-other-planets

The M15 west slope of Main Pit at First Quantum Minerals’ Kansanshi copper–gold mine in Zambia is an actively mined eastward-facing wall. This study highlights the early warning provided by a monitoring service based on interferometric synthetic aperture radar (InSAR). Displacements were detected along the slope face, prompting an intervention using horizontal drains. To monitor the west slope of the pit, visual inspections, ground-based radars (GBRs), robotic total stations (RTS) as well as imagery from the radar satellite constellation TerraSAR-X was used. The early warning alert was issued in July 2022 on InSAR displacements estimated using three months of imagery acquired at 11day intervals. Surface movement was detected on several benches with the displacement beginning at the base of the wall and spreading radially and laterally, resulting in a circular subsidence pattern. This was suspected to be a precursor to a failure along the slope face. There was no alert of anomalous displacements from the GBR and RTS. In response to the observed displacements, a mitigation plan was drawn up onsite. It was hypothesised that the movements were due to increased porewater pressure. Using horizontal drains and boreholes, the area was to be dewatered. The depressurisation drilling began in November 2022 and continued until December 2022 when it was observed that the rate of movement had slowed from 15.1 mm per year to 5.9 mm per year before the onset of the wet season. Controlling the risk and prevention of the failure allowed for the smooth and continued operation of the trolley lines that were installed to reduce diesel usage. Furthermore, other costs associated with the failure—an increase in the tramming distance, for example—were successfully avoided. Using InSAR as a monitoring tool, timely intervention was possible, saving time, quantifiable monetary resources, and increasing operational efficiency.