The Effect of Inclined Pair Piers on Bed Topography: Clear Water, Incipient Motion and Live Bed
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RESEARCH PAPER
The Effect of Inclined Pair Piers on Bed Topography: Clear Water, Incipient Motion and Live Bed Farid Sedighi1 · Mohammad Vaghefi1 · Goodarz Ahmadi2 Received: 25 August 2019 / Accepted: 1 October 2020 © Shiraz University 2020
Abstract In this study, effects of inclined pair piers on bed topography in a scaled river bend were experimentally investigated. Three separate groups of experiments under clear water, incipient motion and movable bed conditions were performed. The results showed that for a pair of V-shaped piers, the scouring was higher for the pier closer to the bend outer perimeter, while the opposite trend was observed for the Ʌ-shaped piers. It was observed that shifting the position of Ʌ-shaped piers from the 60 degree angle to 90 and 120 degree angles led to 6% and 26% increase in the peak scour depth, while, for the V-shaped piers, the position that led to the maximum scour depth varied depending on the flow regime. The maximum scour depth, which was 117% of the flow depth, was observed in the live bed experiment in which the V-shaped piers were placed at the f 60° plane. Under the live bed condition, it was seen that piers closer to the inner bank are less susceptible to scouring. Keywords Inclined piers · 180 degree bend · Live bed · Clear water · Incipient-motion · Bed topography List of Symbols R Central radius B Channel width D Bridge pier diameter ds Maximum scouring depth Fr Froude number h The maximum height of the sediment Re Reynolds number t Time of scour te Equilibrium time of scour σ Standard deviation of sediment θ Angular position of the piers d50 Mean diameter of the sediment d84 Diameter, in millimeters at which 84% of the sediment is finer * Mohammad Vaghefi [email protected] Farid Sedighi [email protected] Goodarz Ahmadi [email protected] 1
Department of Civil Engineering, Persian Gulf University, 7516913817 Bushehr, Iran
Mechanical and Aeronautical Engineering Department, Clarkson University, 8 Clarkson Ave, Potsdam, NY 13699, USA
2
d16 Diameter, in millimeters at which 16% of the sediment is finer y Depth of water at the beginning of the bend U Flow velocity Uc Critical velocity Z Level of the bed W Surrounded rectangle width on the scour hole L Surrounded rectangle length at the scour hole g Acceleration of gravity Gs Specific weight
1 Introduction Bridge piers are constructed with different shapes, and inclination angles and many are located the bends of meandering rivers. Every year, a great number of bridges are destroyed due to scour around piers. This study examined the effects of a pair of inclined piers positioned on different sections of a 180-degree bended channel on the topography of its bed. The flume of the advanced hydraulics laboratory of the Persian Gulf University was used in these experimentations. Due to its critical importance, the effects of bridge piers on scouring have been the subject of numerous studies in the past. Raudkivi and Ettema (1983) compiled the data obtained from several experiments, an
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