Rheological regulation of high-volume fly ash slurry for scour protection of offshore monopile foundations

Offshore wind monopile foundations suffer severe local seabed scouring. High-volume fly ash scour protection (HFSP) slurry is expected to become a novel passive scour protection material. This work developed the slurry composed of OPC, fly ash, alkali-activated sodium silicate solution (ASS) and HPMC. A three-factor four-level orthogonal test was carried out to test fluidity, static anti-dispersion performance and rheological properties, and three classical rheological constitutive models were compared to characterize the fresh slurry flow behavior. Range analysis and multivariate nonlinear regression were adopted to quantify the coupling influence of raw material dosages on the rheological properties with four candidate functional forms compared for each parameter. Results demonstrate that HPMC dominates rheological parameters and underwater anti-dispersion capacity, while simultaneously strengthening its shear-thinning characteristic whereas OPC and ASS play only a secondary role. The H-B model exhibits the best fitting performance and accurately reflects the slurry's nonlinear shear-thinning feature. Nonlinear prediction formulas for core H-B rheological parameters are further established to resolve conflicting performance requirements of the three raw materials. Within the dosage range tested, the coefficients of determination are above 0.97. This study offers quantitative rheological control references for HFSP slurry applied to offshore monopile scour protection.