مطالعه آزمايشگاهي اثر طول آبشكن بر آبشستگي موضعي پيرامون سري آبشكن هاي چوگاني و L شكل

Experimental Study Effect of Length on Local Scouring Around Hockey and L-Shaped Spur Dikes

آﺑﺸﮑﻦﻫﺎ ﺳﺎزه ﻫﺎﯾﯽ ﻫﺴﺘﻨﺪ ﮐﻪ ﺑﺎ ﻫﺪف ﺣﻔﺎﻇﺖ از ﺟﺪاره ﻫﺎي رودﺧﺎﻧﻪ در ﺑﺮاﺑﺮ ﻓﺮﺳﺎﯾﺶ اﺣﺪاث ﻣﯽ ﺷﻮﻧﺪ. اﯾﻦ ﺳﺎزه ﻫﺎ ﺑﻪ ﺻﻮرت ﻋﻤﻮد ﯾﺎ ﺑﺎ زاوﯾﻪاي ﻧﺴﺒﺖ ﺑﻪ ﺟﻬﺖ ﺟﺮﯾﺎن اﺻﻠﯽ و در ﺳﺎﺣﻞ رودﺧﺎﻧﻪ اﺣﺪاث ﻣﯽﺷﻮﻧﺪ. اﺛﺮ ﺧﺼﻮﺻﯿﺎت ﻫﻨﺪﺳﯽ آﺑﺸﮑﻦ ﻫﺎ ﺑﺮ ﺷﮑﻞ ﮔﯿﺮي و ﺗﻮﺳﻌﻪ ﺣﻔﺮه آﺑﺸﺴﺘﮕﯽ در آﺑﺸﮑﻦ ﻫﺎي ﭼﻮﮔﺎﻧﯽ ﺗﺎﮐﻨﻮن ﺑﻪ ﻧﺪرت ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار ﮔﺮﻓﺘﻪ اﺳﺖ. ﭘﮋوﻫﺶ ﺣﺎﺿﺮ ﺑﺎ ﻫﺪف ارزﯾﺎﺑﯽ اﺛﺮ ﻃﻮل آﺑﺸﮑﻦ ﭼﻮﮔﺎﻧﯽ ﺑﺮ ﺷﮑﻞ ﮔﯿﺮي و ﺗﻮﺳﻌﻪ ﺣﻔﺮه آﺑﺸﺴﺘﮕﯽ و ﻣﻘﺎﯾﺴﻪ آن ﺑﺎ آﺑﺸﮑﻦ L ﺷﮑﻞ اﻧﺠﺎم ﺷﺪ. در اﯾﻦ راﺳﺘﺎ، ﺗﻤﺎﻣﯽ آزﻣﺎﯾﺶﻫﺎ در ﺷﺮاﯾﻂ آب زﻻل و ﺑﺎ اﺳﺘﻔﺎده از آﺑﺸﮑﻦﻫﺎﯾﯽ ﺑﺎ ﻃﻮل ﻫﺎي 8 و 12 ﺳﺎﻧﺘﯿﻤﺘﺮ در ﯾﮏ ﻓﻠﻮم آزﻣﺎﯾﺸﮕﺎﻫﯽ اﻧﺠﺎم ﺷﺪ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن داد ﮐﻪ اﺑﻌﺎد ﺣﻔﺮه آﺑﺸﺴﺘﮕﯽ و ﻧﯿﺰ ﻃﻮل و ﺿﺨﺎﻣﺖ ﭘﺸﺘﻪ رﺳﻮﺑﯽ ﺑﺎ اﻓﺰاﯾﺶ ﻃﻮل آﺑﺸﮑﻦ اﻓﺰاﯾﺶ ﯾﺎﻓﺖ. در ﺻﻮرﺗﯽ ﮐﻪ ﻣﻘﺪار اﯾﻦ اﻓﺰاﯾﺶ در آﺑﺸﮑﻦ ﭼﻮﮔﺎﻧﯽ ﮐﻤﺘﺮ از آﺑﺸﮑﻦ L ﺷﮑﻞ ﺑﻮد. ﺑﺎ اﻓﺰاﯾﺶ ﻃﻮل آﺑﺸﮑﻦ ﻫﺎ، ﺑﯿﺸﯿﻨﻪ ﻋﻤﻖ، ﻣﺴﺎﺣﺖ و ﺣﺠﻢ ﺣﻔﺮه آﺑﺸﺴﺘﮕﯽ اﻓﺰاﯾﺶ ﯾﺎﻓﺖ. اﯾﻦ اﻓﺰاﯾﺶ ﺑﻪ ﻃﻮر ﻣﯿﺎﻧﮕﯿﻦ در آﺑﺸﮑﻦﻫﺎي L ﺷﮑﻞ ﺑﺮاﺑﺮ ﺑﺎ 57/5 و 67/7 و در آﺑﺸﮑﻦﻫﺎي ﭼﻮﮔﺎﻧﯽ ﺑﺮاﺑﺮ ﺑﺎ 33/3 و 42 درﺻﺪ ﺑﺮاي دو ﻃﻮل ﻣﺘﻔﺎوت از آﺑﺸﮑﻦ ﻫﺎ ﺑﻮد. ﻫﻤﭽﻨﯿﻦ، در ﻣﻘﻄﻊ ﭘﺎﯾﯿﻦ دﺳﺖ آﺑﺸﮑﻦ ﭼﻮﮔﺎﻧﯽ ﻫﯿﭻ ﮔﻮﻧﻪ آﺑﺸﺴﺘﮕﯽ در ﻣﺠﺎورت دﯾﻮاره ﻓﻠﻮم ﻣﺸﺎﻫﺪه ﻧﺸﺪ. ﺑﻨﺎﺑﺮاﯾﻦ، ﻣﺸﺨﺺ ﮔﺮدﯾﺪ ﮐﻪ اﺑﻌﺎد ﺣﻔﺮه آﺑﺸﺴﺘﮕﯽ ﭘﯿﺮاﻣﻮن آﺑﺸﮑﻦ ﭼﻮﮔﺎﻧﯽ ﮐﻮﭼﮑﺘﺮ از آﺑﺸﮑﻦ L ﺷﮑﻞ اﺳﺖ.

Spur dikes are structures that constructed for protection of the river walls against the erosion. Spur dikes are generally built perpendicular or at an angle to the river bank or revetment, protruding into the watercourse. The effect of the geometrical characteristics of the hockey spur dikes on formation developing of scour hole has been rarely studied. Spur dikes. The current study aims to evaluate the effect of the length of the hockey spur dike on the formation and development of scour hole and comparing with that effect in L-shaped spur dike. In this direction, all experiments were done in clear water conditions using the spur dikes in length of 8 cm and 12 cm and in a laboratory flume. The results asserted that the dimensions of the scour hole and the length and thickness of the sedimentary hill were increased by raising the length of the spur dike. However, this increment was lower in hockey spur dike than the L-shaped spur dike. The maximum depth, area and the volume of the scour hole were also increased by raising the length of the spur dikes. This increment in-average was equal to 57.5 and 67.7 per cent in L-shaped spur dikes and equal to 33.3 and 42 per cent in hockey spur dikes for two different lengths of spur dikes. Furthermore, no scouring was observed in downstream section of the hockey spur dikes near the wall. Therefore, the dimensions of the scour hole around the hockey spur dike was lower than those in the L-shaped spur dikes.