Implementation of Modified Cam-Clay Model using Closest Point Projection Method

Abstract

The modified Cam-Clay model is a widely used constitutive model of soft clay in geotechnical engineering. It can describe the behaviors of soft clay well. Therefore, this model is used in many numerical analyses to get better results. However, many derivations of the integration of the elastoplasticstress are in the p?-q plane which geotechnical engineers are familiar with. In this paper, the closes point projection method is used for integrating the stress of the modified Cam-Clay model. In addition, the plasticity of the model and the equations used in the closest point projection method are deriveddetailedlyunderthe Cartesian coordinate space. Subsequently, a UMAT subroutine of ABAQUS is developed using FORTRAN. Finally, a triaxial test under drainage consolidation with three consolidation states is calculated using the analytical equations, the ABAQUS built-in model, and the UMAT model respectively for verifications. Results show that the proposed method is feasible and stable, and all three types of results using different methods are the same, it is proved that the UMAT model is accurate enough for analyses.