Local Scour Effects on Bearing Capacities of Pile-Disc Composite Foundations under Combined H-T Loads in Sandy Soil
The foundations of offshore wind turbines are often subjected to complex combined loads and the impact of wave-induced scour.The single pile-friction disc composite foundation combines the advantages of single piles and gravity foundations,with the friction disc also acting as an anti-scour plate.To investigate the impact of local scour on the bearing characteristics of the composite founda-tion under combined H-T loads,a series of model load tests were carried out based on indoor flume test apparatus.Load-displacement curves of the pile-disc composite foundation before and after scour were obtained,and after dimensionless processing and curve fitting,the bearing capacity envelope and simplified calculation formula for the H-T joint loaded pile-disc composite foundation were derived.Subsequently,finite element analysis was employed to analyze the impact of key scour parameters(scour depth,scour width,and scour angle)and loading point height on the bearing capacities of the composite foundations.The results showed that:the presence of a scour pit significantly reduced the lateral and torsional resistance of the composite foundation by up to 25％and 45％,respectively.Fur-ther analysis revealed that the bending moment of the pile increased significantly with the height of loading point,and decreased with the increase in pre-applied torque.Local scour markedly reduced the bearing capacity of the composite foundation,with the corresponding bearing capacity envelope under combined H-T loads contracting inward to varying degrees.Among the scour parameters,scour depth had the greatest impact,reducing lateral and torsional resistance by approximately 35％and 60％re-spectively,followed by scour angle,with scour width having the least impact.In addition,the bearing capacity envelope of the pile-disc composite foundation varied to some extent under different loading paths.
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