Experimental Study on Critical Shear Stress of Cohesive Soils and Soil Mixtures

Highlights Erosion tests were performed to study the critical shear stress of cohesive soils and soil mixtures. Linear relationships were observed between critical shear stress and cohesion of cohesive soils. Mixture critical shear stress relates to noncohesive particle size and cohesive soil erodibility. A formula for calculating the critical shear stress of soil mixtures is proposed and verified. Abstract. The incipient motion of soil is an important engineering property that impacts reservoir sedimentation, stable channel design, river bed degradation, and dam breach. Due to numerous factors influencing the erodibility parameters, the study of critical shear stress (τc) of cohesive soils and soil mixtures is still far from mature. In this study, erosion experiments were conducted to investigate the influence of soil properties on the τc of remolded cohesive soils and cohesive and noncohesive soil mixtures with mud contents varying from 0% to 100% using an erosion function apparatus (EFA). For cohesive soils, direct linear relationships were observed between τc and cohesion (c). The critical shear stress for soil mixture (τcm) erosion increased monotonically with an increase in mud content (pm). The median diameter of noncohesive soil (Ds), the void ratio (e), and the organic content of cohesive soil also influenced τcm. A formula for calculating τcm considering the effect of pm and the τc of noncohesive soil and pure mud was developed. The proposed formula was validated using experimental data from the present and previous research, and it can reproduce the variation of τcm for reconstituted soil mixtures. To use the proposed formula to predict the τcm for artificial engineering problems, experimental erosion tests should be performed. Future research should further test the proposed formula based on additional experimental data.