Abstract

The proliferation of land reclamation projects around the world has increased the need for advanced studies on the mechanical behavior of soft clays. One of the most important aspects of soft clay behaviour is the time dependent deformation characteristics. The behavioral characteristics of soft clays suggest that an overstress type soil model is suitable for the analysis of such deposits. A model initially proposed by P. Perzyna has been extended with the addition of a Cam Clay type yield criterion and implemented in a finite element code to analyze geotechnical problems in two dimensions. In addition to describing the monotonic loading behavior, the model is used for the analysis of soft clays under vibrational loads from vehicle traffic. In order to investigate the effects of vibrations on the rate dependent behaviour of soft clays, a new vibrational slump test has been devised. The results are used to explain the processes involved during the deformation of a clay sample under its own weight. It is seen that the variations of the parameters used in the soil model exhibit a marked resemblance to the variations of the fundamental material state variables such as the flow volume, activation energy, and entropy. In the light of this observation, the possible relationships between the material parameters used in the present viscoplasticity model and the thermodynamic variables from rate process theory are discussed. The conclusions drawn from the vibrational slump test results as well as the careful examination of the constitutive model have been implemented in a Finite Element computer code. The predictive abilities of this program have been established by comparison with field measurements and the behavior of a soft clay foundation under the effect of surface vibrations is simulated. It is found that vehicle traffic during and after the construction of landfills (or embankments) noticeably retards the consolidation process and creates prolonged periods of quasi-undrained conditions