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

Abstract

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, τy, 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 τy and their applicability to FGS-CMs is conducted. The constant shear-rate (CSR) test, when conducted at low shear-rate, yields the most accurate τy of FGS-CMs. Subsequently, the results are used to develop a generalized relationship which explains the variation of the τy 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 τy. The results from CR tests were utilized in the development of a novel methodology to determine the elastic component of the shear modulus, GE, 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.