Sand Bed Response to Submerged Water Jet

摘要

Submerged water jets are effective in the displacement of large volumes of seabed sediment for such operations as the de-burial of dropped objects, the burial of pipelines and the preparation of trenches for pipeline laying. The success of such operations depends on an ability to predict the response of the seabed sediment for given sediment and jet characteristics. The paper reports on experiments carried out to investigate the response of sand beds to the action of vertical submerged water jets. The work involves larger jet diameters, finer sediments and smaller jet distances to the bed, resulting in much larger dynamic and static scour holes than in previous laboratory experiments. Dynamic scour hole depth is found to be determined primarily by jet momentum flux with a very weak dependence on sediment size while scour hole diameter is determined both by jet momentum flux and sediment size. The correlation between static scour hole depth and jet momentum flux is poor because of a dependence on the shape and lateral extent of the dynamic scour hole. Empirical equations for scour diameter and dynamic depth are presented. There is a need for field-scale measurements of bed response for greater confidence in predicting bed response during offshore operations.