Rheometric characterization of the fluid mud forming potential of a bay mud

When a cohesive mud bed in a wide estuary or bay yields due to wave action, measurable damping of wave height occurs as energy is absorbed by the highly viscous sediment. In order to assess the fluid mud generating potential of an estuarine mud, controlled oscillatory shear stress tests were carried out in a rheometer on naturally consolidated mud from Suisun Bay in California. Since only one sample was available for testing, three cohesive clays of known compositions and different concentrations were also subjected to oscillatory rheometry. The aim of these tests was to draw conclusions from the rheological behavior of these clays on the yield behavior of the bay mud at a lower than its natural concentration at which this mud is in the liquefied state. Tests on the clays revealed that the so-called flow-point stress characterizing bed yield could be described reasonably well by a simple exponential function dependent on the concentration. This observation permitted the selection of a similar exponential equation for the bay mud as well as delineation of the shallow parts in Grizzly Bay, a sub-embayment, where a potential exists for fluid mud generation and wave damping.