The work described herein is a laboratory study of the scour of clays by two types of jets:​ a submerged vertical circular impinging jet and a submerged plane turbulent wall jet. The scour tests were undertaken using one type of soil composed of 40 % clay, 53 % silt, and 7 % fine sand. The first objective was to examine the characteristics of scour in clay by these jets, including the form of erosion of die clay and the dimensions of the scour hole produced by the jets. The second objective was to develop a method of predicting the scour hole dimensions in a clay from the hydraulic properties of the jet and the properties of the soil.

For the scour by the circular impinging jet, an analysis based on the mechanics of impinging jets shows 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. Equations were developed to predict the scour hole dimensions for the asymptotic or equilibrium state of scour (for a scour hole eroded by mass erosion). A dimensionless scour hole profile was also developed. Measurements showed that the scour hole dimensions appear to grow linearly with the logarithm of time, except at times very near the beginning of scour and as the scour hole nears equilibrium state, as has previously observed in scour by jets in sand. In a similar method as for impinging jet scour, equations were developed to predict the maximum depth of scour, the distance to the maximum depth, the length of the scour hole, and scour hole profile, for scour in a cohesive soil by a plane turbulent wall jet. This work shows that repeatable experiments in the scour by jets of cohesive materials can be performed.