Liquid limit and rheology of clay: insight from diffuse double layer theory

The liquid limit (LL) and yield stress are fundamental properties reflecting the mechanical behaviors and consistency of clays. While their underlying relationship has been previously explored, a unified and quantitative description remains uncertain. This study develops a theoretical framework based on diffuse double layer (DDL) theory to establish their connection and systematically estimate their values across different mineralogy properties including specific surface area (SSA) and cation exchange capacity (CEC) and varying environmental and physicochemical conditions including temperature, salinity, and pH. Yield stress and LL are first derived from interparticle interactions, assuming a parallel particle arrangement. A comprehensive model is proposed to evaluate the liquid limit by incorporating SSA, CEC, and ion valency, which shows superior performance across various soil types. Both LL and yield stress vary linearly with temperature. The observed decreases in LL and yield stress with increasing salt concentration in bentonite are explained by DDL compression, while the complex salinity response in non-expansive soils results from the combined effects of DDL shrinkage and the collapse of a “house-of-cards” microstructure. Across the pH spectrum, both LL and yield stress exhibit minimum and maximum values, attributed to the disappearance of DDL repulsion at the particle isoelectric point (IEP) and a structural transition from non-parallel to parallel particle arrangements near the edge IEP, respectively. The proposed approach provides a unified and physically grounded method for evaluating the consistency limits and rheology of clays, with potential applications in slope stability assessment in sensitive clays, ground improvement, and geohazard evaluation.