CAM CLAY PLASTICITY .2. IMPLICIT INTEGRATION OF CONSTITUTIVE EQUATION BASED ON A NONLINEAR ELASTIC STRESS PREDICTOR

An improved stress integration algorithm for the modified Cam-Clay plasticity model capable of accounting for nonlinear elasticity is proposed. The algorithm entails the use of secant elastic moduli for integrating the nonlinear elastic constitutive equation in conjunction with a fully implicit scheme for calculating plastic strains. Numerical experiments demonstrate the algorithm's good accuracy and stability under a wide variety of imposed stress and strain paths. This algorithm should be useful in situations dominated by combined nonlinear elastic unloading and plasticity such as would occur in tunneling and excavations.