Experimental and numerical study on scour protection effect for pile foundations of sea-crossing bridges

Within the areas of bridge engineering, scour is an important factor contributing to structural vulnerability. To mitigate the local scour of the sea-crossing bridge foundation, systematic experimental and numerical investigations into the scour protection effect of pile groups were conducted. In this paper, through numerical simulation of 11 pile groups for scour protection, the effects of the geometry of the riprap layer under the action of wave–current coupling were explored. Based on the above laws, two protection methods were proposed: multi-layer riprap and sacrificial pile + riprap. The effectiveness of five different protection methods under an actual engineering background was studied through seven sets of physical tests. The results show that, in numerical simulations, the square riprap provides better scour protection than the elliptical riprap; the 2-m-thick square riprap can effectively reduce the maximum scour depth by 89%. In physical scale tests, the unprotected experimental results are consistent with the numerical simulations and standard formulas; riprap protection can reduce the scour equilibrium time, and the square riprap provides better scour protection; finally, the 2-m-thick multi-layer riprap not only minimizes the maximum scour depth within the pile group, but also maintains the stability of the protective structure. The research results can provide a reference for practical projects considering scour protection under wave–current coupling.