Hydrodynamic effects of porous baskets on scour patterns at elliptical and hexagonal piers

This study investigates the effectiveness of a newly introduced scour countermeasure, the porous basket (PB), in modifying flow structure and mitigating scour around elliptical and hexagonal piers with varying length-to-width ratios (l/w). Experimental analysis of near-bed flow velocities revealed a significant reduction at the pier face, followed by velocity recovery after reattachment in the second half of the pier for both geometries. However, in elliptical piers, lateral imbalances in vortex shedding and flow separation led to localized variations in velocity profiles, while l/w had no influence on the location of flow separation. The results indicate that piers with l/w = 5 ratio experienced 50% reduction in scour volume due to lower Reynolds Shear Stress (RSS) in the downflow region. In general, increasing l/w resulted in a more confined scour area and reduced scour volume. Implementation of the PB, effectively trapped over 65% of turbulence kinetic energy (TKE), significantly reducing scour at the pier base. As turbulence dissipated and flow stabilized, RSS values approached zero. Among the tested installation distances, the smaller placement exhibited the best scour mitigation performance by enhancing localized turbulent energy dissipation. This finding highlights the potential of the PB in improving bridge pier stability and reducing local scour effects.