Experimental study of grouting protection against local scouring of monopile foundations for offshore wind turbines

Local scouring is a severe threat to the safety of offshore wind turbines, and it cannot be eliminated completely by traditional protection methods. In this paper, to improve seabed scouring resistance, a new local scouring countermeasure—grouting protection—is proposed, and flume scouring tests are reported. It is found that after grouting, the micro-morphological characteristics of the soil are changed, with the internal friction angle and cohesion of the seabed soil being improved significantly. The grouted seabed has different modes during the development of scouring, i.e., cracking, peeling off, incipient motion, and abrasion. Further analysis shows that the critical shear stress of grouted seabed particles is much greater than that of ungrouted ones, and the ultimate scouring depth of grouted seabed is much lower than that of ungrouted seabed. The protective effect of grouting on local scouring is fully verified: compared with collar protection, grouting protection is more reliable under weak hydrodynamic action, and compared with riprap protection, grouting protection is more efficient under extreme hydrodynamic action.