Numerical and theoretical verification of modified cam-clay model and discussion on its problems

Isotropic consolidation test and consolidated-undrained triaxial test were first undertaken to obtain the parameters of the modified cam-clay (MCC) model and the behavior of natural clayey soil. Then, for the first time, numerical simulation of the two tests was performed by three-dimensional finite element method (FEM) using ABAQUS program. The consolidated-drained triaxial test was also simulated by FEM and compared with theoretical results of MCC model. Especially, the behaviors of MCC model during unloading and reloading were analyzed in detail by FEM. The analysis and comparison indicate that the MCC model is able to accurately describe many features of the mechanical behavior of the soil in isotropic consolidation test and consolidated-drained triaxial test. And the MCC model can well describe the variation of excess pore water pressure with the development of axial strain in consolidated-undrained triaxial test, but its ability to predict the relationship between axial strain and shear stress is relatively poor. The comparison also shows that FEM solutions of the MCC model are basically identical to the theoretical ones. In addition, Mandel-Cryer effect unable to be discovered by the conventional triaxial test in laboratories was disclosed by FEM. The analysis of unloading-reloading by FEM demonstrates that the MCC model disobeys the law of energy conservation under the cyclic loading condition if the elastic shear modulus is linearly pressure-dependent.