In this study, a set of rules is established, which when implemented in the modeling of dilatant soils, within the framework of associative plasticity, enables very successful shear and dilatancy predictions. The proposed approach is based on a number of principles, the most important of which are: (1) The plasticity model must have a loading surface that hardens kinematically, and a failure surface that is perfectly plastic. (2) Experimental evidence shows that uniformly deformed sand samples dilate with a constant rate when they reach their ultimate strength value, while critical state is only achieved at very large strains. There is a unique point A on the loading surface that corresponds to the experimentally observed dilatation rate. The hardening rule must, therefore, ensure that the stress point approaches A as it approaches the failure surface. These principles are implemented in a plasticity model and compared to numerous published monotonic and cyclic tests, with varied stress paths, performed on a true triaxial apparatus. The agreement between experimental data and theoretical predictions is excellent.
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