Application of portable free-fall penetrometer for geotechnical investigation of Arctic nearshore zone

Abstract

The Arctic is currently undergoing rapid changes with regard to sea ice extent permafrost thaw, and coastal erosion. In addition to hydrodynamic processes, the sediments in the Arctic nearshore zone are affected by freeze–thaw cycles, as well as an increase of abundant suspended sediment introduced by permafrost-induced mass movements, such as retrogressive thaw slumps, and increased river discharge. During the YUKON14 expedition to Herschel Island, Yukon, in situ geotechnical testing of nearshore zone sediments was conducted using a portable free-fall penetrometer. Approximately 200 sites were tested, and four different geotechnical signatures identified and grouped. Most locations were characterized by a soft sediment top layer that exhibited a noticeably lower sediment strength than the underlying sediment. In some cases, multiple layers of different sediment strength were detected in the upper meter of the seabed surface. The results were correlated to existing sediment grain size records and backscatter information from a phase measuring bathymetric sonar. Strong spatial variations in sediment type and stiffness were observed, as well as in abundance and thickness of a top layer of very soft and loose sediment. The geotechnical signatures were correlated to site-specific hydrodynamic conditions, morphology, and vicinity to thaw slumps.