Rheological Characteristics of Fine-Grained Soil-Slurries

Various natural and man-made scenarios such as rainfall-induced terrestrial landslides, offshore landslides, mudflows, and transportation of mud by pipelines and dredging activities involve fine-grained soils, minerals, and sediments with very high moisture contents (i.e., the slurry state). Presumably, the behavior of these materials in their slurry state falls within a transition between the solid-dominant and liquid-dominant zones. Hence, investigations to establish the rheological properties of these materials (i.e., defining their flow and deformation characteristics) in this transition phase become mandatory. With this in view, investigations were conducted to establish the grain-water interaction that would govern the rheological characteristics of these materials in their slurried states. The study takes into account the effect of state parameters like water content, w (which is indicative of the concentration of solids), and soil-specific parameters (viz, mineralogy, liquid limit [LL], specific surface area [SSA], and the pore solution characteristics). Based on a critical analysis of the variation of the plastic viscosity, n(p), with respect to w, a hypothesis for the phase-transition mechanism of the slurries, from visco-plastic to ideal-plastic regime, has been proposed. It has been demonstrated that such a hypothesis facilitates understanding of the grain-water interaction for a wide range of water content and associated changes in the rheological behavior. Furthermore, it has been demonstrated that there exists a unique relationship between and yield stress, tau(y), with the parameter "normalized water content," w(n) (= w/LL), for these materials. It is the authors' belief that these relationships would be useful in obtaining parameters such as slurry viscosity, yield stress, and optimal/limiting water content, which are required in the design of various industrial applications involving flow, the pumping of fine-grained soil-slurries, or both.