Unified Critical‐State Bounding‐Surface Plasticity Model for Soil

An isotropic plasticity model for soil is presented that introduces a number of significant modifications into an existing bounding‐surface model for clay to extend the range of application to sand, offering a simple unified treatment for soil. The paper focuses on the modeling of sands. The new features are both radial and deviatoric mapping rules to define the loading surface, a nonassociated flow rule incorporating a subelliptic plastic potential surface, and the presence of a kinked critical‐state line. Unlike many existing macroscopically based models, loose and dense states of a specific sand are not given different sets of material constants since the two states are linked by means of an “effective” normal consolidation line. Thus, for instance, sand in a dense state is considered very heavily overconsolidated in the normal mean effective‐stress range. After presenting the normalized triaxial formulation in full and discussing the calibration procedure, comparisons are made between the model's simulations and compression test data from established drained and undrained triaxial experiments up to failure on loose and dense sand over a wide range of confinements.