Experimental and numerical investigations of scours around a rectangular pile cap using a horseshoe-shaped collar

ABSTRACT Local scours around the bridge pier are a common phenomenon in the mobile riverbed, leading to a substantial risk of bridge failures. In this study, the primary objective is to present a protective collar of pile foundations on the basis of flow structure and riverbed erosion. For this purpose, model experiment cooperating with numerical simulations under sandy water conditions was applied to investigate the changes in scour patterns around the rectangular pile cap, and the influence of flow velocity and riverbed height on the scour area and depth was analyzed under conditions without protective measures. On this basis, a horseshoe-shaped collar defined by the elliptical equation was proposed to mitigate the scour on the riverbed. The results show that the scour patterns calculated by computational fluid dynamics are similar to those with experimental methods, the maximum relative deviation of the scour area and depth are 9.16 and 23.94%, respectively. The simulation method can evaluate the rationality of anti-scouring collar designs. The comparison of topography indicates that scour around the foundation is effectively mitigated with a protective collar; the maximum scour area decreased by 64.85-85.52% for different conditions. The scour depth was significantly reduced, with a minimum reduction of 66.67%.