Settlements at several masts of the power line constructed on sedimentary permafrost deposits in Sisimiut, West-Greenland: Field- and lab work, data processing and thermal modelling

Abstract

The electricity of Greenland’s second largest town, Sisimiut (West -Greenland), is supplied by a hydropower plant, located some 20 km north from the town. In late 2021, Nukissiorfiit – the Greenland public utilities company – observed severe settlements of some power line masts, constructed on fine-grained ice rich permafrost. These settlements threaten the integrity of the power lines and may potentially result in a disruption of power supply to the town. This project investigates the cause of these settlements with an aim to suggest appropriate adaptation measures. Frozen soil samples were retrieved from around one of the masts at the south shore of the Second Fjord in Sisimiut, and soil temperatures are measured at nine locations. At each location, the soil temperature is measured at depths of approximately 20 cm and 1 m below surface. Furthermore, the air temperature and the temperature of the metal mast foundation is monitored. Finally, four Electric Resistivity Tomography (ERT) profiles were collected and the whole site was surveyed by a drone that provided detailed Digital Elevation Models (DEM) and orthophotos of the area. The collected frozen soil samples were further processed in the laboratories of the Technical University of Denmark in Kgs. Lyngby, and they show a stratigraphy consisting of an organic peat top layer, followed by ice rich silt and clay layers at depth. The soil sample information and temperature data is used to set up and calibrate a thermal model using the software GeoStudio TEMP/W. This model is used to investigate several possible solutions to stabilise the masts under current and future climate conditions. The solutions studied comprise the construction of an elevated gravel pad around the foundation of the masts, or alternatively the use of thermosyphons to stabilize the soil thermal regime. The effect of constructing the gravel embankment with and without EPS insulation in the pad is considered as well. Lastly, the eventual influence of the considered adaptation methods on the future thermal regime is compared with the model output where no measures are taken at all.

The electricity of Greenland’s second largest town, Sisimiut (West -Greenland), is supplied by a hydropower plant, located some 20 km north from the town. In late 2021, Nukissiorfiit – the Greenland public utilities company – observed severe settlements of some power line masts, constructed on fine-grained ice rich permafrost. These settlements threaten the integrity of the power lines and may potentially result in a disruption of power supply to the town. This project investigates the cause of these settlements with an aim to suggest appropriate adaptation measures. Frozen soil samples were retrieved from around one of the masts at the south shore of the Second Fjord in Sisimiut, and soil temperatures are measured at nine locations. At each location, the soil temperature is measured at depths of approximately 20 cm and 1 m below surface. Furthermore, the air temperature and the temperature of the metal mast foundation is monitored. Finally, four Electric Resistivity Tomography (ERT) profiles were collected and the whole site was surveyed by a drone that provided detailed Digital Elevation Models (DEM) and orthophotos of the area. The collected frozen soil samples were further processed in the laboratories of the Technical University of Denmark in Kgs. Lyngby, and they show a stratigraphy consisting of an organic peat top layer, followed by ice rich silt and clay layers at depth. The soil sample information and temperature data is used to set up and calibrate a thermal model using the software GeoStudio TEMP/W. This model is used to investigate several possible solutions to stabilise the masts under current and future climate conditions. The solutions studied comprise the construction of an elevated gravel pad around the foundation of the masts, or alternatively the use of thermosyphons to stabilize the soil thermal regime. The effect of constructing the gravel embankment with and without EPS insulation in the pad is considered as well. Lastly, the eventual influence of the considered adaptation methods on the future thermal regime is compared with the model output where no measures are taken at all.