PROGRESSIVE
*Shear Box Data PIPE SOIL 
Soil materials have a pronounced nonlinear behaviour, and correct numerical simulation requires sophisticated constitutive models including a relatively large number of parameters and complicated calibration procedures. Occurrence of strain localization at large shear deformation further complicates the numerical modeling. Strain localization is not a continuum phenomenon. It is characterized by a lengthscale. Therefore for properly addressing of this phenomenon, a model should include the concept of lengthscale either through mesh dimensions (adaptive meshing) or special provision in the constitutive model. However both methods has not yet become of practical usage. In this study a relatively straightforward nonassociated MohrCoulomb soil constitutive model implemented in the finite element commercial program ABAQUS/Standard is customized to account for progressive mobilization (hardening/softening) of soil shear strength parameters, f and c, during shear involving large deformations. The procedure used in this study for estimating hardening/softening behaviour of dense and loose sand is based on the results of direct shear box (DSB) tests as illustrated in Figure 1. First, based on the results of DSB tests performed on dense sand under different confining stresses (Figure 1a), the mobilized shear strength parameters are calculated and expressed as functions of the box displacements (Figures 1b & 1c). Next, finite element simulations of the DSB tests are carried out to find out a correspondence between measured horizontal displacements and state variables defining the material behaviour – the plastic strain magnitude was selected here (Figure 1d & 1e). Finally, the mobilized shear strength parameters are expressed as functions of the plastic strain magnitude (Figure 1f). Based on a good match between numerical predictions and experimental observations, it is assumed that average values of shear strength, as measured in DSB tests, can be used for inferring the hardening/softening rules shown in Figure 1f. The resulting hardening/softening rules are verified against fullscale test results in a soil/structure interaction problem. Based on this approach, hardening/softening curves for a dense sand are provided for use in geotechnical applications. 

