بررسي آزمايشگاهي تاثير موقعيت پايه روي آبشستگي موضعي اطراف پايه پل در قوس 90 درجه ملايم

Laboratory Study of Pier Location on Scouring Around Bridge Pier in 90-Degree Mild Bend

ﭘﻞﻫﺎ از ﺟﻤﻠﻪ ﻣﻬﻤﺘﺮﯾﻦ و ﭘﺮﮐﺎرﺑﺮدﺗﺮﯾﻦ ﺳﺎزهﻫﺎي رودﺧﺎﻧﻪاي ﻫﺴﺘﻨﺪ ﮐﻪ ﻫﺮ ﺳﺎﻟﻪ ﺑﺎ وﻗﻮع ﺳﯿﻼب ﺗﻌﺪاد زﯾﺎدي از آﻧﻬﺎ ﺗﺨﺮﯾﺐ ﻣﯽﺷﻮﻧﺪ. آﺑﺸﺴﺘﮕﯽ ﻣﻮﺿﻌﯽ اﻃﺮاف ﭘﺎﯾﻪﻫﺎي ﭘﻞ از ﺟﻤﻠﻪ ﻋﻮاﻣﻞ ﻣﻮﺛﺮ در اﯾﻦ ﺗﺨﺮﯾﺐﻫﺎ اﺳﺖ. در اﯾﻦ ﺗﺤﻘﯿﻖ ﺑﺮاي ﺑﺮرﺳﯽ ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ در اﻃﺮاف ﭘﺎﯾﻪ ﭘﻞ در ﻗﻮس رودﺧﺎﻧﻪ، آزﻣﺎﯾﺶﻫﺎﯾﯽ در ﯾﮏ ﻓﻠﻮم آزﻣﺎﯾﺸﮕﺎﻫﯽ ﺑﺎ ﻗﻮس 90 درﺟﻪ ﺑﺎ ﻧﺴﺒﺖ3/7 =𝑅𝐶⁄𝐵 و از ﺟﻨﺲ ﭘﻼﮐﺴﯽ ﮔﻼس و ﻓﻮﻻد اﻧﺠﺎم ﭘﺬﯾﺮﻓﺖ. ﺑﺪﯾﻦ ﻣﻨﻈﻮر ﺑﺎ ﻗﺮار دادن ﯾﮏ ﭘﺎﯾﻪ اﺳﺘﻮاﻧﻪاي ﺑﻪ ﻗﻄﺮ 45 ﻣﯿﻠﯽﻣﺘﺮ در زواﯾﺎي 45 ،30 و 60 درﺟﻪ در ﻃﻮل ﻗﻮس ﭘﺪﯾﺪه آﺑﺸﺴﺘﮕﯽ ﺣﻮل ﭘﺎﯾﻪ در ﺣﺎﻟﺖ آب زﻻل و 3 ﻋﺪد ﻓﺮود ﺟﺮﯾﺎن ﺑﺮرﺳﯽ ﺷﺪ. ﺑﺮاي ﻣﺼﺎﻟﺢ ﮐﻒ ﻓﻠﻮم از ﻣﺎﺳﻪ ﻃﺒﯿﻌﯽ ﺑﺎ ﻗﻄﺮ ﻣﺘﻮﺳﻂ 0/85 ﻣﯿﻠﯽﻣﺘﺮ اﺳﺘﻔﺎده ﺷﺪ. ﻧﺘﺎﯾﺞ اﯾﻦ ﺗﺤﻘﯿﻖ ﻧﺸﺎن داد ﮐﻪ ﺣﺪاﮐﺜﺮ ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ ﻫﻨﮕﺎم ﻧﺼﺐ ﭘﺎﯾﻪ اﺳﺘﻮاﻧﻪاي در ﻃﻮل ﻗﻮس ﻣﺘﻔﺎوت ﺑﻮده و ﺑﺎ اﻓﺰاﯾﺶ دﺑﯽ ﺟﺮﯾﺎن در ﮐﻠﯿﻪ ﻣﻮﻗﻌﯿﺖﻫﺎ، ﻋﻤﻖ و ﺣﺠﻢ ﭼﺎﻟﻪ آﺑﺸﺴﺘﮕﯽ ﻧﯿﺰ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ. ﻫﻤﭽﻨﯿﻦ ﺣﺪاﮐﺜﺮ ﻋﻤﻖ و ﺣﺠﻢ آﺑﺸﺴﺘﮕﯽ در ﻧﯿﻤﻪ دوم ﺧﻢ در زاوﯾﻪ 60 درﺟﻪ و ﺣﺪاﻗﻞ ﻋﻤﻖ و ﺣﺠﻢ آﺑﺸﺴﺘﮕﯽ در ﻣﯿﺎﻧﻪ ﺧﻢ در زاوﯾﻪ 45 درﺟﻪ رخ ﻣﯽدﻫﺪ. در ﻧﻬﺎﯾﺖ ﻣﺸﺎﻫﺪه ﮔﺮدﯾﺪ ﮐﻪ ﺗﻮﺳﻌﻪ ﭘﺸﺘﻪ رﺳﻮﺑﯽ ﺑﻌﺪ از ﭘﺎﯾﻪ و ﻣﯿﺰان ﮔﺴﺘﺮش آن در ﻧﯿﻤﻪ اول ﺧﻢ ﺑﯿﺸﺘﺮ از ﻧﯿﻤﻪ دوم آن ﺑﻮد. ﻋﻼوه ﺑﺮ اﯾﻦ ﻧﺘﺎﯾﺞ اﯾﻦ ﺗﺤﻘﯿﻖ ﻧﺸﺎن داد ﺣﺪاﮐﺜﺮ و ﺣﺪاﻗﻞ ﻣﻘﺪار ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ ﻧﺴﺒﺖ ﺑﻪ ﻗﻄﺮ ﭘﺎﯾﻪ ﺑﻪ ﺗﺮﺗﯿﺐ ﺑﺮاﺑﺮ ﺑﺎ 2/24 و 1/22 ﻣﯽ ﺑﺎﺷﺪ.

Bridges are the most useful structures on rivers which floods cause damage to them every year. One of the known factors in bridges destruction is local scouring around the bridge piers. In this study, to investigate the scour depth around the bridge pier in the river bend, experiments were performed in a laboratory flume with a 90-degree bend with . By placing a cylindrical pier with a diameter of 45 mm at three locations of 30, 45 and 60 degrees along the bend, for three flow Froude numbers, the scouring around the pier under clear water condition was investigated. Natural sand with an average diameter of 0.85 mm is used for the bed materials. The results showed that the maximum scour depth around the bridge pier varies at a different location along the bend. Besides, the flow discharge increase grows the depth and volume of the scour hole at all positions. Additionally, maximum and minimum depth and volume of scouring hole occurs in the second half of the bend at 60- degree position and in the middle of the bend at 45- degree position, respectively. Finally, it was recorded that the development of the sedimentary hill after the pier and its extent in the first half of the bend was higher than the second half of bend. The result also indicated that the maximum and minimum scour depths relative to the pier diameter are equal to 2.24 and 1.22, respectively.