كنترل آب‌شستگي موضعي توسط طوقه‌هاي متقارن و نامتقارن در اطراف پايه پل در قوس رودخانه‌ها

Control of local scour by symmetrical and asymmetrical collar around the bridge pier in river bend

وﻗﻮع آبﺷﺴﺘﮕﯽ در اﻃﺮاف ﭘﺎﯾﻪ ﻫﺎي ﭘﻞ ﯾﮑﯽ از ﻋﻤﺪه ﺗﺮﯾﻦ دﻻﯾﻞ ﺗﺨﺮﯾﺐ ﭘﻞﻫﺎ اﺳﺖ. ﯾﮑﯽ از روشﻫﺎي ﮐﺎﻫﺶ آبﺷﺴﺘﮕﯽ اﻃﺮاف ﭘﺎﯾﻪﻫﺎي ﭘﻞ ﻧﺼﺐ ﻃﻮﻗﻪ ﻣﺤﺎﻓﻆ ﺑﺮ روي ﭘﺎﯾﻪ اﺳﺖ.ﺑﺮاي اﯾﻦ ﻣﻨﻈﻮر ﺟﻬﺖ ﺑﺮرﺳﯽ اﺛﺮ ﻃﻮﻗﻪ ﯾﮏ ﺳﺮي آزﻣﺎﯾﺶ در ﯾﮏ ﻓﻠﻮم آزﻣﺎﯾﺸﮕﺎﻫﯽ ﺑﺎ ﻗﻮس 180درﺟﻪ و ﺷﻌﺎع ﻣﺮﮐﺰي 2/8ﻣﺘﺮ و ﻋﺮض 0 /6ﻣﺘﺮ ﺑﺎ 4/67= R/Bاز ﺟﻨﺲ ﭘﻼﮐﺴﯽ ﮔﻼس اﻧﺠﺎم ﭘﺬﯾﺮﻓﺖ. در اﯾﻦ ﺗﺤﻘﯿﻖ ﺑﺎ ﻗﺮار دادن ﯾﮏ ﭘﺎﯾﻪ ﺑﻪ ﻗﻄﺮ 5ﺳﺎﻧﺘﯽﻣﺘﺮ ﺑﻪ ﻫﻤﺮاه ﻃﻮﻗﻪﻫﺎي ﻣﺨﺘﻠﻒ ﺑﻪ ﻃﻮل ﻧﺴﺒﯽ در ﺑﺎﻻ دﺳﺖ و ﭘﺎﯾﯿﻦ دﺳﺖ 0/4، 0/6، 0/8و 1در ﻣﻮﻗﻌﯿﺖ 70 درﺟﻪ ﻗﻮس ﺑﺎ دﺑﯽ ﺛﺎﺑﺖ 16ﻟﯿﺘﺮ ﺑﺮ ﺛﺎﻧﯿﻪ و ﻋﻤﻖ ﺛﺎﺑﺖ 12ﺳﺎﻧﺘﯽﻣﺘﺮ ﭘﺪﯾﺪه آبﺷﺴﺘﮕﯽ ﺣﻮل ﭘﺎﯾﻪ در ﺣﺎﻟﺖ آب زﻻل ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار ﮔﺮﻓﺖ. ﺑﺮاي ﻣﺼﺎﻟﺢ ﮐﻒ ﻓﻠﻮم از ﻣﺎﺳﻪ ﻃﺒﯿﻌﯽ ﺑﺎ داﻧﻪ ﺑﻨﺪي ﯾﮑﻨﻮاﺧﺖ ﺑﺎ Dm=2 mmو ﺿﺮﯾﺐ ﯾﮑﻨﻮاﺧﺘﯽ 1/8اﺳﺘﻔﺎده ﺷﺪ. ﻧﺘﺎﯾﺞ اﯾﻦ ﺗﺤﻘﯿﻖ ﻧﺸﺎن داد ﺑﺎ اﻓﺰاﯾﺶ ﻃﻮل ﻧﺴﺒﯽ ﻃﻮﻗﻪ در ﺑﺎﻻ دﺳﺖ و ﭘﺎﯾﯿﻦ دﺳﺖ ﻣﯿﺰان آبﺷﺴﺘﮕﯽ ﻣﻮﺿﻌﯽ در اﻃﺮاف ﭘﺎﯾﻪ ﺑﻪ ﻃﻮر ﻣﻼﺣﻈﻪاي ﮐﺎﻫﺶ ﻣﯽﯾﺎﺑﺪ و ﻫﻤﭽﻨﯿﻦ ﺑﯿﺸﺘﺮﯾﻦ و ﮐﻤﺘﺮﯾﻦ درﺻﺪ ﮐﺎﻫﺶ در ﻋﻤﻖ آبﺷﺴﺘﮕﯽ در اﻃﺮاف ﻃﻮﻗﻪ ﺑﺎ ﻃﻮل ﻧﺴﺒﯽ ﺑﺎﻻ دﺳﺖ و ﭘﺎﯾﯿﻦ دﺳﺖ ﺑﻪ ﺗﺮﺗﯿﺐ 68و 12 ﺑﺪﺳﺖ آﻣﺪه اﺳﺖ.

Scouring around the bridge piers is one of the main reasons for the destruction of bridges. One of the methods to reduce scouring around the bridge piers is installing a protective collar on the base. For this purpose, to investigate the effect of the collar, a series of experiments in a laboratory flume with an bend of 180 degrees and a central radius of 2.8 meters and a width of 0.6 meters with R / B = 4 was made of Plexiglas. In this research, by placing a base with a diameter of 5 cm with different collars of relative length upstream and downstream 0.4, 0.6, 0.8 and 1 in the position of 70 ° bend with a constant flow of 16 liters Per second and a constant depth of 10 cm. The scouring phenomenon around the base in the state of clear water was investigated. Natural sand with uniform granulation with Dm = 2 mm and uniformity coefficient of 1.8 was used for canal floor. The results of this study showed. Increasing the relative length of the collar upstream and downstream significantly reduces the amount of local scour around the base and also the highest and lowest percentage of reduction in scour depth around the collar with the relative length of upstream and downstream, respectively, 68 and 12 has been achieved.