Rapid sediment mapping and in situ geotechnical characterization in challenging aquatic areas

摘要

Yakutat Bay, Southeast Alaska, is characterized by significant spatial variations in sediment type and dynamics. The northwestern side is supplied by sediments from the nearby glaciers, and is affected by longshore sediment transport processes, while the southeastern side has no direct sediment input, and is affected by human activities. In situ seabed investigations can be difficult, and expensive, due to logistical challenges in such remote locations. A portable free fall penetrometer (PFFP) was deployed 149 times along 16 transects in water depths of 2-48 m. The deceleration and pore pressure records during the probe's penetration into the seabed were used to characterize the surficial sediments. Equivalents of quasi-static bearing capacity were determined using the deceleration-depth signatures, and yielded strong variabilities ranging from 5 to 107 kPa at sediment depths of 10.3-41.9 cm. Correlating the PFFP results to visual field observations and literature, a regional classification scheme, and an updated sediment distribution map were derived. The pore pressure response was correlated to the different sediment types, and was used to assess the sediment's consolidation state. At the northwestern side, an increasing pore pressure trend indicated underconsolidated cohesive sediments. At the southeastern side, clayey sediments appeared to be more consolidated except of sediments of high organic content near the populated areas. The use of the pore pressure measurements represents a novel way for rapid sediment characterization using PFFP. The presented approach to create rapidly a regional sediment classification scheme offers a time- and cost-effective method to derive seabed sediment maps in areas of difficult access and logistics.