Critical shear stress for erosion of sand and mud mixtures

The critical shear stress for erosion of sand and mud mixtures is theoretically investigated and expressed as a function of the critical shear stresses of pure sand and mud, mud content, and sand diameter. The proposed formula accounts for different structures and behaviours of the mixtures with low and high mud contents. The critical shear stress of pure mud is related to the solid/void volume ratio, and this relation is extended to the mud component in the mixture to consider the effect of compaction. It is found that the mud dry density, not the mixture dry density, is a direct factor affecting the mixture erosion. The developed formula has been calibrated and tested using four sets of experimental data collected from the literature. It reproduces the variations of the critical shear stress and mud dry density well.