Application of a Critical State Model for Cyclic Loading of Sands

The purpose of the current paper is to extend a critical state constitutive model presented previously for sand behavior under monotonic loading such that it can predict behavior under cyclic loads as well. Due to the use of the critical state soil mechanics framework, the original model was able to predict sand behavior over a wide range void ratios and confining pressures, and take into account various aspects of behavior of loose and dense sands, including inherent and stress-induced anisotropies, softening and liquefaction of sands under monotonic loads. Extension of the base model for cyclic loading is accomplished through the use of bounding surface plasticity. Yield surface of the original model is used as the bounding surface of the new model, and also its loading surface using a deviatoric mapping rule. A new hardening modulus is used that enables predicting the behavior during loading and unloading. Flow rule of the original model is also modified in order to enable better prediction of the loading-unloading behavior, especially after phase transformation. Predictions based on this model showed satisfactory match with observed behavior of sands over a wide range of void ratios and confining pressures in drained and undrained monotonic and cyclic loading.