Fluidized solidified slurry diffusion range and local scour protection effectiveness around a monopile: a laboratory investigation for an offshore wind farm in Eastern Zhejiang Province, China

Local scour threatens monopile foundations, while the construction-stage washout and post-curing stability of fluidized solidified slurry remain insufficiently quantified. This laboratory study evaluates slurry diffusion and fragmentation at upstream, side, and downstream grouting positions and assesses the protection provided by a cured slurry layer. A 1:100 recirculating-flume model representing an offshore wind farm in eastern Zhejiang Province was tested at flow-intensity ratios V/Vc of 0.31 and 0.60; an unprotected scour test and a protected live-bed test up to V/Vc = 1.65 were also conducted. At V/Vc = 0.31, the slurry showed no flow-induced fragmentation at any grouting position. At V/Vc = 0.60, fragments from upstream and side grouting travelled up to 10.7D and 14.9D downstream, respectively, whereas the downstream-grouted mass remained largely stable. The side-grouting response coincided with an amplified bed-shear-stress zone extending approximately 1.2D transversely and 1.1D streamwise. The unprotected test produced a maximum scour depth of approximately 0.35D and a horizontal extent of about 2D. Under live-bed conditions at V/Vc = 1.65, the cured 2D-radius protection layer lost 0.88% of its mass and retained its structural integrity. By linking grouting position to pile-induced hydrodynamics and evaluating both construction and post-curing stages, the study provides site-bounded evidence for grouting-position selection and protection-extent design under steady-current conditions.