Development of a _nite deformation elasto!plastic model for pressure sensitive materials is presented[ The chosen model\ which has its roots in the MRS!Lade material model is in~uenced by recent developments[ The thermodynamic consequences of introducing non!associative yielding "both deviatoric and volumetric# and hardening:softening characteristics are assessed[ The consistently linearized Algorithmic Tangent Sti}! ness "ATS# tensor is presented[ This tensor is used in the constitutive driver as a key feature of the e.cient iterative procedure for satisfying equilibrium in the case of stress "or mixed# control[ The chosen model is calibrated using data from experiments conducted in a Directional Shear Cell "DSC#\ which has been used extensively at the University of Colorado at Boulder to investigate the behavior of pressure sensitive materials under deformations of large magnitude[ ร 0887 Elsevier Science Ltd[ All rights reserved[ Key words] Hyperelasto!plasticity^Large deformations^Geomaterials^Finite element analysis Corresponding author[ Tel[] 990 204 157 3324^fax] 990 204 157 6874^e!mail] jeremicรpolaris[clarkson[edu 0 In the most ideal situation when the material is preconsolidated isotropically[