Investigation of The effect of immerse vanes installation on scouring around the bridge abutment

Background and Objectives: The scouring of river bed around bridge is one of the most important issues in bridges destruction. It has been found that the occurrence of scouring on the bridges abutment is the most important cause of the destruction of bridges in all countries. Among the techniques of reducing scouring around the bridge abutment which are called “indirect measures” is to modify the flow pattern and reduce the power of vortex vortices which are the main cause of scour. At the present study the performance of immerse vanes was investigated at a constant distance of 2 times of the abutment effective length and 4 different angles under four different flow conditions (Froude numbers= 0.15, 0.17, 0.2 and 0.22 (. The destruction of immerse vanes is impossible due to the installation of them above the bed and within the depth of the flow. As a result, the main purpose of this study is to determine the most suitable angle of displacement of the vanes in the upstream of the bridge abutment, which will cause the least scouring.
Materials and Methods: The experimental tests were conducted in a flume of 8 meters long and 1 meters wide. A rectangular abutment was installed at the middle of the test section (2 meters long) covered with bed of fine sand. Each test started by turning on the pump, which transfers the flow from the reservoir below the laboratory. The water flows through the flume after passing through a net that is filled with fibers in order to depreciate the flow fluctuations. At the end of the flume, after passing through the sliding valve, the flow into the pool was collected. At the end of the pond, a 53-degree triangular overflow was placed in order to measure the flow rate, which then flows into the underground reservoir. At the beginning of each experiment, after the leveling of the bed by opening the opening at the beginning of the flume, the flow gradually entered the flume so that the sediment would not be destroyed. After increasing the water level in the flume, the flow rate slowly increases to reach the desired flow rate.
Results: In this study, bed topography was taken for all experiments using laser meter and then plotted using Surfer software. The results showed that in all experiments, maximum scour depth was observed in the upper nose of the abutment, and with increasing flow conditions, due to increased bed shear stress and the power of vortices around the structure, the maximum scour depth and scour hole volume increased. Also in this study, it was found that the angle of installation of the immerse vans has a great effect on the performance of the vanes in reducing the depth, surface and volume of the scouring hole. Generally, it shows that use of immerse vanes have been reduced scouring significantly compared to the case of no vanes.
Conclusion: The most effective angle of installation was found to be equal to 65 degrees, which, on average, reduced the maximum depth of scouring, lenght and width by 66, 71 and 69 percent, respectively.