Small-strain shear modulus and yielding characteristics of compacted high-plasticity clay

This experimental study describes the elastic and yielding response of compacted high-plasticity clay in conjunction with deformation characteristics at relatively larger strains for different stress paths and stress states. K₀ consolidated undrained triaxial compression and extension stress path tests were conducted on compacted Nagpur cohesive soil with bender element measurements to explore the elastic and yielding response of soil. The experimental results showed that the stress path direction had a significant impact on the stress–strain–strength properties of soil as the peak deviatoric stress was found to increase with the increase in stress path angle. The measured small-strain shear modulus (G_max) values were observed to be a function of the mean effective stress (p′) with slight dependency on deviatoric stress (q). G_max was found to reduce with increase in strain level during shearing. An attempt was made to formulate an empirical correlation for compacted cohesive soil based on the elastic shear stiffness in pre-yield conditions. This correlation was further used to determine the yielding criteria of compacted cohesive soil along with the other two well-established criteria of stress–strain and strain energy.