Scour of Cohesive Soil by Submerged Circular Turbulent Impinging Jets

This paper introduces a method for estimating the scour in cohesive soils produced by a submerged vertical circular turbulent impinging jet. Determining scour in cohesive soils is a complex problem, partly because the clay particles within the soil are held together by electrochemical forces that are not easily quantifiable. As well, erosion occurs in many forms, such as the removal of individual particles or as large chunks of soil. Results of a laboratory study of scour by a circular impinging jet of a cohesive soil, consisting of 40% clay, 53% silt, and 7% fine sand, are presented. Analysis based on the mechanics of the impinging jets shows that the dimensions of the scour hole at an equilibrium state of scour are a function of the momentum flux from the jet, the impingement height (for “large” impingement heights), the viscosity and density of the eroding fluid, and the critical shear stress of the soil. Mass erosion was the predominant type of erosion observed.