Yield curves of sand in a particle-crushing region were determined by a multi-step stress path method under triaxial compression and extension stresses. The yield curves were found to have the characteristic dq/dp equals G( eta ), irrespective of the stress path, where q is the deviator stress, p, the effective mean principal stress and eta , the stress ratio. By using the relationship between dq/dp and eta , families of yield curves were depicted in both compression and extension stress regions. Based on a new expression for energy dissipation per unit volume, a yield curve equation was derived and this equation was proved to be well comparable with the experimental curve. An equation for predicting the stress-strain relation was also presented.
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