Three Dimensional Implementation And Verification Of HISS Model In ABAUQS

In the numerical analysis of the nonlinear behavior of soil materials, the mostpopular elasto-plastic constitutive models used are the capped models. There are twomain shortcomings in all these capped models. First, the yield surfaces of these cappedmodels are composed of two or more surfaces, consequently the normal direction isusually non-unique at the intersections involved in multiple yield surfaces, and specialnumerical treatment is needed as these models are implemented. Secondly, most of thecapped models involving failure or critical surfaces with yield cap intersections allowdilation only after the peak stress is reached. Based on the cohesionless materials, Desaiproposed a hierarchical single surface model with a smooth single surface, which avoidscomputational difficulties associated in dealing with intersections of multiple yieldsurfaces. Moreover, it allows dilation before peak stress as it occurs in many geologicmaterials.Taking δ1model which was proposed by Desai, and considers isotropic hardeningand non-associate flow rule for example, the properties of the hierarchical single surfacewere discussed in this paper. Influences of parameters on the yield surface wereanalyzed and the stress paths and changes of yield surface during aloading-unloading-reloading circle were measured by MATLAB. Based on the furtherdevelopment platform provided by ABAQUS, the δ1model was programmed byFORTRAN into a three dimensional user-defined material subroutine (UMAT), whichcan be used in ABAQUS.Several triaxial tests with different stress paths (hydrostatic compression,conventional triaxial compression, triaxial compression and triaxial extension tests) andfive proportional loading tests of Leighton Buzzard Sand and Munich Sand weresimulated by ABAQUS calling the UMAT developed in this paper. The stress-strainrelationships predicted by numerical simulation showed good agreement with the onesobserved in laboratory tests by Hashmi, which verified the UMAT and the applicabilityof the hierarchical single surface model to describe the mechanical behavior of sand.The stress states of all the points are the same in soil cell tests, and the stress state issingle and clear. In order to check the applicability of the UMAT to analyze practical engineering problems, the forced deformation problem with complicated stress state ofa foundation under a strip footing was simulate by ABAQUS. The results predicted byABAQUS were also compared with the ones observed in physical model test by Hashmi,and they showed good agreement in the stress field. At last, the forced deformation of apavement was calculated by ABAQUS to preliminarily demonstrate the potentialapplication of the UMAT in real three dimensional boundary problems.On this contribution, the δ1model of the HISS model which was proposed byDesai was first programmed into a three dimensional user-defined material subroutine,and its implement in ABAQUS was accomplished. Also, the three dimensional UMATwas verified and the applicability of HISS to describe the mechanic behavior of sandswas checked, which shows the potential of the UMAT to solve practical engineeringproblems. The three dimensional implement of the δ1model provides a new constitutiverelationship for ABAQUS to analyze the three dimensional elasto-plastic problems ofsoils.