Amirkabir University of Technology Amirkabir Journal of Civil Engineering 2588-297X 52 8 2020 10 22 Effect of Concurrent Use of the Six-Legged Element and Rip-Rap for Scour Control with Economic Considerations Effect of Concurrent Use of the Six-Legged Element and Rip-Rap for Scour Control with Economic Considerations 1995 2010 3419 10.22060/ceej.2019.15793.6032 FA Mohammad Rashki Ghaleh Nou Ph.D Student- Hydraulic structures- Dep. of Civil Engineering- University of Sistan and Balouchestan- Zahedan 0000-0002-3923-0511 Mehdi Azhdary Moghaddam University of Sistan and Baluchestan Mahmood Shafai Bajestan Prof. Faculty of Water Science Engineering, Shahid Chamran University of Ahvaz Hazi Mohammad Azamathulla Professor of Civil & Environmental Engineering, The University of the West Indies, St. Augustine Campus, Trinidad Journal Article 2019 02 08 The scour control downstream of the ski-jump spillways is one of the most important issues encountered by hydraulic engineers. In this paper, an experimental investigation was performed to evaluate the reduction in the maximum volume of the scour hole due to the concurrent use of the six-legged concrete elements (A-Jacks) and rip-rap materials in different hydraulic conditions. These elements were placed in the downstream of the ski-jump spillway. The experiments included a single size of concrete element and two sizes of rip-rap with five flow discharges and three tail-water depths. The change in tail-water depth resulted in the spillway having free, semi-submerged and submerged conditions. The results were showed that as scour depth increased, the scouring rate is significantly reduced. By simultaneous usage of concrete elements and rip-rap materials, the maximum scour volume decreased up to 100% in different hydraulic conditions as compared to the control tests. In addition, the results showed that the use of a rip-rap layer is about 80% cheaper than the coating with six-legged elements, which this difference is reduced by increasing the thickness of rip-rap layer. The scour control downstream of the ski-jump spillways is one of the most important issues encountered by hydraulic engineers. In this paper, an experimental investigation was performed to evaluate the reduction in the maximum volume of the scour hole due to the concurrent use of the six-legged concrete elements (A-Jacks) and rip-rap materials in different hydraulic conditions. These elements were placed in the downstream of the ski-jump spillway. The experiments included a single size of concrete element and two sizes of rip-rap with five flow discharges and three tail-water depths. The change in tail-water depth resulted in the spillway having free, semi-submerged and submerged conditions. The results were showed that as scour depth increased, the scouring rate is significantly reduced. By simultaneous usage of concrete elements and rip-rap materials, the maximum scour volume decreased up to 100% in different hydraulic conditions as compared to the control tests. In addition, the results showed that the use of a rip-rap layer is about 80% cheaper than the coating with six-legged elements, which this difference is reduced by increasing the thickness of rip-rap layer. https://ceej.aut.ac.ir/article_3419_4a533591763dfa743a13affab1a85793.pdf