A NON-ASSOCIATIVE CAM-CLAY PLASTICITY MODEL FOR THE STRESS-STRAIN-TIME BEHAVIOR OF SOFT CLAYS

The objective of this study was to develop an improved numerical model for the stress-strain-time behavior of soft clays. This work is based upon a general phenomenological model developed over the past decade by Kavazanjian and Mitchell which is based upon patterns of soft clay behavior generally accepted by geotechnical engineers. The numerical model is a modification of a Cam-Clay type plasticity model previously developed by Borja to conform to this general phenomenological model.; It is assumed in the constitutive model that the deformation of soft clays can be separated into a time independent immediate component and a time dependent delayed component. Each component is composed of interdependent volumetric and deviatoric contributions. The time independent component is governed by the ellipsoidal modified Cam-Clay volumetric yield surface and an interdependent horizontal deviatoric yield surface beneath the ellipsoid. The time dependent behavior is incorporated by allowing creep strain and quasi-preconsolidation pressure to develop.; The constitutive model was coded into a finite element program CLAY2D, which is a derivative of Borja's program SPIN2D. CLAY2D was then used to perform parametric studies on Weald clay and San Francisco Bay Mud to evaluate the predictive capability of the numerical model. The numerical results are shown to have excellent agreement with published laboratory test results. Major improvements on the prediction of deviatoric strains and or pore pressure response over SPIN2D were observed.; The time dependent behavior of soft clay in one-dimensional compression was extensively investigated after the predictive capability of the numerical model was established. Numerical results for subjects of current interest and controversy, including the effects of sample size, preconsolidation and load increment ratio on consolidation behavior and the dependency of rate of secondary compression on overconsolidation ratio and deviatoric stress level are presented. Based upon the numerical results presented in this dissertation, it is concluded that this model is capable of predicting the time-dependent pore pressure and deformation behavior of saturated soft clays with low to intermediate sensitivity for a wide range of geotechnical problems.