James K. Mitchell, 1992. "Characteristics and Mechanisms of Clay Creep and Creep Rupture", Clay-Water Interface and its Rheological Implications, P. F. Low, J. K. Mitchell, G. Sposito, H. van Olphen, N. Güven, R. M. Pollastro
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Time-dependent deformations, such as creep and secondary compression, and time-dependent stress changes at constant deformation, such as stress relaxation, are important considerations in many geotechnical engineering studies. Practical situations in which these effects are important include long-term settlements of structures on compressible ground, deformations of earth structures, movements of natural and excavated slopes, and squeezing of soft ground around tunnels. Although methods for the analysis and prediction of one-dimensional and three-dimensional time-dependent consolidation of clay soils have been available for many years and have met with reasonable success in engineering practice, present ability to describe and predict time-dependent deformations and stress relaxations under deviatone (shear) stress states properly is very limited. Most analyses are made to determine limit equilibrium conditions; i.e., conditions at failure, or stress-deformation responses without consideration of time. Accordingly, the study of the rheological characteristics of clays at states of most interest in geotechnical engineering, i.e., in the consistency range from the plastic to the liquid limit, remain of great research interest.
Research on time-dependent deformation and stress phenomena in soils is important not only because of the immediate direct application of the results to analyses of practical problems, but also because the results of such studies can be used to obtain fundamental information about clay structure, interparticle bonding, and the mechanisms controlling strength and deformation behavior. In addition, the studies provide a basis for the formulation of constitutive relationships that can be used in analytical or numerical analyses of earth-system behavior.The purpose of th is chapter
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Rheology is the science of the flow of fluids and deformation of solids. Of special interest to the clay scientist are the flow behavior and stability of clay suspensions, and the time-dependent deformation of clays in a solid or semi-solid state. The physical state of a clay may change with increasing water content; from a solid, to a semi-rigid plastic, then to a gel, and finally to a suspension. In each state, the main factors determining the rheological behavior of the system are related to: (a) the molecular configuration and dynamics of the clay-water interface, and (b) the nature of the particle interactions at this interface. The hydration of the ions and the clay surfaces plays a special role in clay rheology because flow and deformation directly involve molecular movements along the clay-water interface.