Bridge local scour has long been identified as the most critical cause to bridge failures. Countermeasures that are commonly used nowadays still have disadvantages to some extent. This work is among one of the ongoing efforts to explore reliable alternatives. Inspired by the streamlined body of boxfish and blue shark, this study introduced streamlining features to the bridge piers in order to reduce the erosive forces locally. Based on the excess shear stress criteria, the Reynolds-Averaged Navier Stokes (RANS) numerical model was employed to optimize the streamlined features through parametric studies. The maximum bed shear stress around the optimal streamlined pier was shown to be reduced by ~34% as compared to that around a non-streamlined pier. Further simulation using the advanced Detached Eddy Simulation (DES) model revealed that the streamlined pier also helped reduce the locally turbulence dynamics, which played a significant role in local scour. A set of small-scale flume tests were then conducted in the laboratory to characterize the flow physics and scour behavior of uniform Ottawa sand around piers with various streamlined extents. The experimental results further confirmed the effectiveness of pier streamlining in scour reduction. The maximum scour depth around the streamlined pier was reduced by ~66% as compared to that around a non-streamlined pier. Through monitoring the pore pressure response within sand, the role of vortex-induced excess pore pressure that plays in the scour mechanism was discussed. The vortex-induced excess pore pressure also helped to partially account for an interestingly counterintuitive observation from an independent experiment: the local scour resistance was a slightly decreasing function of the granular bulk density. Finally, a CFD-DEM (Discrete Element Model) two-way coupled model was established to simulate the scour behavior of uniform spherical particles around an oblong pier. The two-phase model successfully captured the characteristic local scour behaviors, and thus may serve as a platform of great potential to further investigate the scour mechanism at microscale in the future. Tremendous efforts were also made to review applications of the emerging two-phase numerical models to the broad flow-induced erosion problems.
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