Experimental study on a tracked underwater remediation technique for scour around offshore wind turbine monopile

Local scour around offshore wind turbine (OWT) monopiles endangers foundation stability. This study investigates a tracked underwater remediation technique that integrates tracked operating equipment and underwater mixed soil to realize layered backfilling and controllable grouting. The underwater mixed soil consists of cement–sodium silicate dual-liquid grout and waste sand-washing slurry. At the selected binder content of 20%, the developed material achieved a 28-day UCS of approximately 920 ± 23 kPa, with satisfactory early-age strength and anti-dispersion performance. A nominal 1:5 geometrically scaled model test was conducted to evaluate equipment performance under complex scour-pit terrain. The maximum sinkage measured in the model test was 2.8 cm, and both pitch and roll angles remained below 10°. After remediation, the density of the central layer reached approximately 1.85 g/cm 3 . Jet scour tests indicated no sustained material detachment or local collapse during the 5-min test stage at the maximum non-failure jet velocity of 4.6 m/s. A conceptual time-strength-trafficability framework was established for repeated-pass planning. These findings provide preliminary evidence for the laboratory-scale feasibility and application potential of the proposed technique.