Field investigations at the NGTS permafrost site: Methodologies, experiences, and results

This paper presents the results of field investigations conducted during the establishment of the permafrost site of the Norwegian GeoTest Sites (NGTS) project. The soil investigation methods used include total sounding, drilling, and sampling with a conventional auger and core and piston sampling. The installation methods for measuring ground temperatures with thermistor strings are also presented. Field investigations and instrumentation have allowed the characterization of continuous soil profiles under rather challenging geotechnical conditions at the site, with layers that include cryopegs. The quality of the retrieved core samples is sufficient for proper characterization of the presence of ground ice and determination of the soil composition and provide specimens that can be used for uniaxial compression tests. The chosen methodologies and results of this field investigation may be of interest to other investigators who are planning work under challenging conditions at sites with saline soils and/or permafrost settings, where the soil is a few degrees below the freezing point and unfrozen soils are present in the strata. In addition, to complete the geocryological characterization of the site, measurements of permafrost temperatures at the site from 2018 to 2024 are presented.