Document Type : Original Article
Authors
1
Department of Water Engineering, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran.
2
Department of Water Engineering, Shahrekord University, Shahrekord, Iran.
3
Department of Water Engineering , Shahrekord University, Shahrekord , Iran.
4
Department of Water Engineering , Shahrekord University , Shahrekord, Iran.
Abstract
Objective: The objectives of this research were: Investigating the effect of the presence of floating objects on scour around the bridge piers. 2- Laboratory investigation of the effect of a gap below the bed surface in a square bridge pier on reducing scour depth in the presence of floating objects. 3- Presenting an equation to consider the effect of a gap below the bed surface on reducing scour depth in the presence of floating objects.
Method: In this study, the effect of creating a subsurface gap in a square pier with a sharp tip on reducing the scour around the bridge pier, where a rectangular floating object is trapped behind the pier, was experimentally investigated. The study was conducted on 2 piers, one with a gap and one without, 3 floating objects (in positions above the water surface, at the water level, and below the water surface), and 4 flow rates (10, 20, 30, and 40) liters per second. A gap of (18+7 cm) was created in the pier, with 7 centimeters of the gap length placed within the bed.
Results: For the base without a gap without the presence of an object, the depth of the washout pit increased with the increase in flow rate, and after placing the object behind the base, it was observed that the increase in the flow rate increases the depth of the washout. The closer the object is to the water surface, the scour around the base decreases and vice versa. The closer the object is to the surface of the bed, the deeper the scour increases. The scour depth increased with the increase in flow rate, and in examining the effect of the size of the floating object, the scour depth increased as the size of the floating object increased. Increasing the flow rate enhances both the depth and volume of the sinkhole. Accumulation of floating objects around the bridge base increases the depth and volume of the sinkhole compared to the absence of floating objects. Creating a gap is an efficient method to control erosion around the bridge pier.The pier, with a gap of 7 cm below the surface of the bed up to 40.8% compared to the control sample, controls erosion around the base.
Conclusions: The results from 80 experiments indicate a reduction in scour by up to 40.8 percent compared to the control sample; therefore, the use of the gap helps control scour around the pier.
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