Relating fine-grained sediment consolidation to acoustic seabed surveying

Abstract

The process of fine-grained seabed sediment consolidation is governed by a variety of factors including grain size distributions, organics, sediment dynamics, and anthropogenic activities (e.g., marine traffic and dredging). Poorly consolidated sediments are typically softer and more susceptible to mobility from shear, while over consolidated sediments are typically stiffer with a higher threshold for mobility from shear. Knowledge of the state of consolidation of seabed sediments is important to assess and maintain navigable depth, predict length scales of seafloor roughness, and assess seabed-object interaction (e.g., anchors, unexploded ordnance). For example, the porosity varies significantly for the same type of sediment for different states of consolidation. Variability is expected and has been qualitatively demonstrated in acoustic seabed surveying including high- and low-frequency techniques. In this study, seabed sediments were characterized using a portable free fall penetrometer along with geotechnical and sedimentological laboratory testing of fine-grained seabed sediments. Testing results quantified both sediment textural (e.g., bulk density, water content, void ratio, and porosity) and strength properties (e.g., undrained shear strength and consolidation state and behavior) and were related to the backscatter intensity observed with different high- and low-frequency off-the-shelf acoustic surveying devices.