Yield stress investigation of mud from Port of Felixstowe (United Kingdom) in view of nautical bottom implementation

Abstract

Purpose: Ports worldwide apply different criteria to define navigability, commonly based on density thresholds, yield stress limits, or a combination of both. These criteria are port specific. In the present article, the characterization of the fluid mud found in the Port of Felixstowe (UK) is provided in view of the implementation of a nautical bottom approach. Methods: One-meter sediment cores were collected in the Port of Felixstowe using a Frahmlot sampler and sub-sampled into fluid mud, pre-consolidated, and consolidated layers. Yield stress, bulk density, particle size distribution and organic matter content were measured on the collected samples and compared with data from other ports. The yield stresses as measured in the laboratory were compared with in-situ yield stress measurements in the port. Results: The laboratory analysis shows limited spatial variation of mud in the Port of Felixstowe, while revealing differences in the yield stress-density relation when compared with mud from other ports. The data are also compared with data previously acquired in the Port of Felixstowe. The differences found are attributed to an improper estimation of density measured by the RheoTune. Conclusion: This study focuses on the characterization of the mud from the Port of Felixstowe. It was found that the mud has a yield stress that is lower, for a given density, than other ports. The yield stresses measured in situ using a RheoTune are in agreement with the Bingham yield stresses as measured in the laboratory, while the densities found using the RheoTune are underestimated relative to the laboratory values. The different types of yield stresses, obtained using different rheological protocols, are related to each other, enabling the comparison between in-situ monitoring and laboratory measurements.