Formation And Motion Characteristics Of Fluid Mud And Counter Measurements

The research on the fluid mud is rather difficult, mainly caused by the shortage ofdata from the field survey and lab experiments. And sometimes, the phenomena offluid mud in the harbor basin and channel cannot be explained well. To determine theconditions of formation, basic characteristics and rules of variation, and to proposecounter measurements further, many field surveies and lab experiments focusing onthe fluid mud were conducted. The field surveies included fluid mud depth, density,process of consolidation or disappearing, and hydrodynamic conditions during largewind and so on. And the lab experiments mainly focused on the granular distribution,rheology, incipient motion, consolidation, fluxion of the fluid mud, as well as theheight of submerged dike. Firstly, the results show that the sufficient cohesivesediment resource is the basic condition for the fluid mud formation. And the bed willbe liquefied with the large wind wave continuous disturbing, meanwhile, a highturbidity layer about0.5m height near bottom would be created, which can move asdensity current or with the tidal current to the channel and deposite to be fluid mud.Secondly, the research on the basic characteristics of fluid mud indicates that theBinham yield stress increases exponentially with the mud density. The critical stressof sediment incipient motion is about0.1-1.0Pa for the mud with density of1050~1400kg/m~3, and the relationship is also exponential. Thirdly, the study on thewhole characteristics of fluid mud motion presents that the interface of fluid mud andabove layer water will be instable due to the turbulent shear of flow, and theentrainment occurs, when the Richardson number is smaller than10. And the ersioncofficent increases with the sediment concentration, which is about0.005~0.03kg/m~2/s for the deposited mud in the channel of Lianyungang, China. Thefluid mud will flow along the bed slop under the action of pressure gradient andgravity. Based on these research results, the processes of fluid mud motion wereexplained in the half-surrounding harbor basin and channel for example Taishan port,as well as the open channel such as Lianyungang port. Lastly, the results of study onthe counter measurements to the fluid mud show that the height of submerged dikemay be0.2-0.5times of water depth. And the technique of nautical depth is one of the most efficient methods to settle the problem of impeding navigation caused by fluidmud. The formulas established in this paper can be used to calculate the verticaldistribution of muddy shoal density, rheological parameters, critical stress of sedimentincipient motion, vertical profile of critical stress, entraiment velocity, erosioncofficent, height of submerged dike and so on. And the data, especially the preciousdata obtained from the field survey may be the basin of further study on the fluidmud.