Single-stage wet sieving: an optimized protocol for rapid and accurate particle size analysis of fine-grained soils

• Theoretical: A single-parameter gradation equation links clay content to gradation parameters via Yue's fabric-sieving mechanism. • Methodological : A single-stage wet sieving protocol that simplifies the process, enhances efficiency, and reduces cost while maintaining accuracy. • V alidation: (1) Both sieving methods yield more clay than hydrometer; (2) Single-stage matches multi-stage accuracy with superior efficiency. • Engineering : Provides a standardized, rapid, and cost-effective method for soil gradation, resolving the precision-complexity trade-off in existing techniques. In the testing methodologies for particle size distribution (PSD) of fine-grained soils, standard sedimentation techniques (e.g., the hydrometer method) and wet-sieving approaches (e.g., the pioneering nylon cloth sieving method developed by Professor Yue Zhongqi’s team) constitute established technical frameworks. While the former offers operational simplicity, it achieves this at the cost of accuracy limitations. The latter, though delivering high precision, may face efficiency challenges due to its multi-stage sieving procedure. To advance streamlined process development, this study integrates fundamental wet-sieving principles with theoretical innovations in gradation curve modeling to propose a single-parameter optimized protocol: (1) Based on previous research on gradation equations and Yue’s fabric-sieving mechanism, the paper establishes a mathematical relationship between clay content and gradation parameters to derive a single-parameter gradation equation; (2) This equation enables experimental redesign, reducing the existing multi-stage wet sieving to a single-stage process; (3) Validation testing on Lanzhou loess (Gansu Province) and Handan expansive soils (Hebei Province) compares the PSD curves derived from the hydrometer method, the multi-stage wet sieving method (Yue’s protocol), and the single-stage wet sieving method proposed in this paper. Furthermore, validation using Shanghai soil data (Yue’s team) corroborates the method’s robustness, showing excellent agreement between predicted and measured PSD curves. The results demonstrate that clay contents measured by both wet sieving methods are significantly higher than those obtained via the hydrometry method. The multi-stage and single-stage sieving method achieve comparable accuracy. The single-stage wet sieving method significantly enhances testing efficiency while reducing operational costs relative to the multi-stage wet sieving method. These findings validate the applicability and superiority of the proposed method for rapid gradation analysis of fine-grained soils. This work represents a significant refinement to the wet-sieving methodology, providing a new pathway for rapid acquisition of fine-grained soil gradation curves in engineering practice.