Geotechnical Investigation of Fine-Grained Top Layer Stratification in the York Estuary, Virginia

Seafloor, estuarine, and lacustrine bed surface sediments are often highly mobile, as well as affected by biogenic effects, geochemical, and geomechanical processes. Thus, sediment composition and texture can change on a variety of temporal and spatial scales, leading potentially to significant uncertainties regarding geotechnical properties and soil behavior of the top layer sediments relevant to sediment transport processes, habitat evolution, as well as engineering and naval applications. Geotechnical investigations of soft top layer sediments have been hampered by the lack of in-situ testing tools and high quality sampling mechanisms. In this study, a portable free fall penetrometer was used for in-situ testing, and sediment sampling was performed using gravity coring, box coring, diver samples, and a prototype sediment sampler as an add-on unit to the portable free fall penetrometer. Sediment samples were then investigated with regards to their sedimentology as well as soil behavior. For the latter, a new field vane shear device was tested. The study area includes different sites of varying environmental conditions in the York River estuary. Field testing and sampling was carried out between 2017 and 2019. Here, the results are presented with focus on data quality from the different methods, seafloor top layer stratigraphy, and the resulting effects on soil behavior. Special attention is given to the question as to whether the top layer sediment soil behavior can be described as a soft soil or rather the top layer follows the characteristics of a viscous fluid. Finally, the potential impacts on sediment transport processes, habitat characteristics, and engineering and naval applications are discussed.