Complex-Fluid Approach for Determining Rheological Characteristics of Fine-Grained Soils and Clay Minerals

Soft and semisolid states of fine-grained soils and clay minerals (FGS-CMs) are frequently dealt with during execution of infrastructure projects located in the coastal areas, analysis of natural hazards, and mineral processing. In most of these cases, the FGS-CMs flow like a slurry, and hence determination of their rheological characteristics becomes essential. However, test methods and approaches available for determining the rheological behavior of the FGS-CMs when they transform from the solid to the liquid state are yet to evolve. This study uses a parallel-plate rheometer, which is widely used for rheological characterization of complex fluids (i.e., fluids which exhibit yield stress), to determine the rheological parameters (i.e., yield stress, ${\tau }_y$, and strains) of the FGS-CMs with a consistency near the liquid limit. A critical analysis of the existing protocols that are used to determine ${\tau }_y$ and their applicability to FGS-CMs is conducted. The constant shear-rate (CSR) test, when conducted at low shear-rate, yields the most accurate ${\tau }_y$ of FGS-CMs. Subsequently, the results are used to develop a generalized relationship which explains the variation of the ${\tau }_y$ of the FGS-CM with the consistency represented as water content normalized with respect to the liquid limit. Furthermore, to understand the nature of strains that develop during the preyielding regime of FGS-CMs, creep-relaxation (CR) tests are conducted by imposing stress equivalent to different fractions of ${\tau }_y$. The results from CR tests were utilized in the development of a novel methodology to determine the elastic component of the shear modulus, $G_E$, of FGS-CMs. This study reveals that FGS-CMs behave as a linear elastoplastic material in the preyield stage, contrary to the much expected purely elastic response, providing a new insight in the realm of contemporary geomechanics.