The definition of yield for bonded materials

Summary In this paper the different definitions of yield for bonded materials are reviewed. It is suggested that yield should be defined based on changes in stiffness from the tangential stiffness versus axial strain graph. Comparisons are made with a recent framework proposed by Jardine and good agreement is shown between Jardine's approach and that presented here, in respect of an initial yield and a final yield point. However, based on data from natural and artificially bonded soils, an additional yield point, that of second yield, is identified where a major drop in stiffness is initiated. In the past the identification of final yield has been used to identify the border between two modes of failure for the shear behaviour of a bonded soil. The first mode is defined when shearing at low confining stresses and the bonded material's strength is greater than that of the destructured soil. A second mode is defined when shearing at high confining stresses where its strength is unaffected by the bonds. In this paper, based on the identification of the second yield, a new transitional mode of failure is clarified at intermediate stresses, where although the soil yields at the initial stages of shearing, it still demonstrates strengths higher than those of the destructured soil due to the post-yield influence of the bonds.