Mitigating scour around bridge piers in alluvial channels using inclined collars

Abstract

Effective mitigation of scour around bridge piers is crucial not only for ensuring structural stability but also for managing the morphological changes in rivers. This study investigates the effectiveness of various collar configurations in mitigating local scour around a cylindrical bridge pier, focusing on the impact of collar inclination and position on scour reduction. Experiments were conducted in a laboratory flume, examining the effects of two collar positions including at the bed-level and buried, four orientations including horizontal, upward, downward, and sideward, and four collar vertical inclination angles including 0°(horizontal), 15°, 30°, and 45°. The maximum scour hole depth, volume, and area, and its longitudinal profile were compared with a baseline no-collar condition. The 15° downward inclined buried collar achieved the largest reductions, with maximum scour depth decreasing by approximately 47.14 % compared to the no-collar setup, 25.40 % compared to the horizontal collar at bed level, and 15.53 % compared to the horizontally buried collar. The 15° upward inclined collar was also effective, though slightly less so than the downward inclination. Results also indicate that the 15° upward and downward inclined buried collar provided the most substantial reductions in scour volume and scoured-bed area compared to the no-collar condition. These reductions underscore the ability of inclined collars to minimize both the depth and lateral spread of scour, providing a more comprehensive mitigation solution. The study also includes a comparative analysis with existing models and introduces a newly developed regression-based equation that outperforms previous models, providing a more reliable tool for practical applications. These findings highlight the potential of tailored collar designs to enhance scour protection around bridge piers, with implications for improved structural resilience in hydraulic engineering.