Experimental Investigation of the Effects of Slotted Cone-Shaped Piers on Scour Reduction Due to Steady Flows
- Razieh Mehrzad (Sahand University of Technology) | Habib Hakimzadeh (Sahand University of Technology)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- September 2017
- Document Type
- Journal Paper
- 318 - 325
- 2017. The International Society of Offshore and Polar Engineers
- conical pier, slotted pier, experimental models, Scour reduction
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Local scouring at bridge piers can be regarded as one of the main reasons for bridge collapses at river crossings. Bridge failure can cause severe damages and can result in serious injury or death. Hence, the investigation of the control of scouring at bridge piers plays an important role in bridge design. The main aim of this study was to evaluate the effectiveness of the slotted conical-shaped piers in reducing local scour when compared with a circular-shaped pier. Two sets of experimental tests were carried out under clear water conditions for the duration of eight hours and with relatively uniform sediments. For the first set, the model piers with different lateral slopes were tested, and the experimental results showed that the maximum scour depth was mainly reduced by a decrease in the lateral slope of the model piers. With the mildest lateral slope angle of 78.69° the maximum scour depth was reduced by as much as 32%. In addition, the combination of the slotted and conical shape could further reduce the maximum scour depth by up to 55%. Thus, the experimental results showed that the combination of the slotted and conical shape can be regarded as a very effective countermeasure tool against local scouring at bridge piers.
There are many reports about the failure of bridges around the world due to the scouring process. These reports clearly show the motivation of this study of scouring and any possibility of scour reduction. The used methods of controlling the scour around bridge piers can be divided into two categories including direct and indirect methods. The first methods may be achieved by the increase in the streambed resistance. This is usually done by placing a riprap layer around the bridge piers (Worman, 1989; Yoon et al., 1995; Chiew, 2008). Indirect methods, however, can be achieved by changing the flow pattern around the piers. These methods may be done, for instance, by the use of a collar around the pier or alternatively by the use of a slot within the pier. Another method in the second category is to use a section of variable depth.
Application of Cone-Shaped Structure with Respect to Side Slope
Sumer et al. (1994) measured the bed shear stress for a cone-shaped structure to observe the influence of the side slope on the shear stress amplification. They found that the overall effect of the side slope in front of the cone-shaped structure was the reduction of the bed shear stress. Sumer and Fredsoe (1997) measured scour around a cone-shaped structure in a follow-up study. The results revealed that the scour mainly decreases through the reduction of the side slope. The scour-reduction efficiency of conical piers has already been established by Sumer and Fredsoe (2002) and confirmed numerically by Besharati and Hakimzadeh (2008). However, the projected area (the blockage ratio) of the conical piers was reduced when compared with that of the cylindrical piers. This reduction was due to the decrease in the lateral slopes in the structures at both the experimental and numerical model piers.
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