مطالعه آزمايشگاهي آبشستگي اطراف گروه پايه كج مستقر بر گروه شمع

Experimental Investigation of Scour around Inclined Bridge Piers Group Based on Piles Group

در تحقيق حاضر تغييرات عمق آبشستگي اطراف گروه پايه كج مستقر بر گروه شمع در شرايط مختلف تراز ﮐﺎرﮔﺬاري و ﺿﺨﺎﻣﺖ ﺳﺮﺷﻤﻊ، آراﯾﺶ و ﻗﻄﺮ ﺷﻤﻊﻫﺎ، ﺑﻪﺻﻮرت آزﻣﺎﯾﺸﮕﺎﻫﯽ ﺑﺮرﺳﯽ ﺷﺪ. ﮔﺮوه ﭘﺎﯾﻪ ﻣﻮرد ﺑﺮرﺳﯽ ﻣﺘﺸﮑﻞ از دو ﭘﺎﯾﻪ ﮐﺞ ﻣﺴﺘﻄﯿﻠﯽ ﺑﻮد ﮐﻪ ﺑﺎ زاوﯾﻪ 28 درﺟﻪ ﺑﺮ روي ﺳﺮ ﺷﻤﻊ ﻧﺼﺐ ﮔﺮدﯾﺪ. آزﻣﺎﯾﺶﻫﺎ روي ﮔﺮوه ﺷﻤﻊﻫﺎ ﺑﺎ ﻗﻄﺮﻫﺎي ﻧﺴﺒﯽ )ﻧﺴﺒﺖ ﻗﻄﺮ ﺷﻤﻊ ﺑﻪ ﻗﻄﺮ ﭘﺎﯾﻪdP / D ( 0/6 و 0/9، در آراﯾﺶ 2×2 و 2×3 و ﺑﺮاي دو ﺿﺨﺎﻣﺖ ﻧﺴﺒﯽ ﺳﺮ ﺷﻤﻊ TPC / D و 1/4و 0/9 و ﻧﯿﺰ ﺗﺮازﻫﺎي ﻧﺴﺒﯽ ﻣﺨﺘﻠﻒ ﮐﺎرﮔﺬاري ﺳﺮ ﺷﻤﻊ 0/5 ،1 ،1/5 ، Z / Tp ﺻﻔﺮ و در ﺣﺎﻟﺖ ﻣﺪﻓﻮن 1/2 و 0/7 - اﻧﺠﺎم ﺷﺪ. ﻣﻘﺎﯾﺴﻪ ﻧﺘﺎﯾﺞ ﺑﯿﺸﯿﻨﻪ ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ ﻧﺸﺎن داد ﮐﻪ ﺑﺎ ﺗﻐﯿﯿﺮ آراﯾﺶ ﺷﻤﻊﻫﺎ از 2×2 ﺑﻪ 2×3 ﺑﻪﻃﻮر ﻣﺘﻮﺳﻂ ﻣﻘﺪار ﺑﯿﺸﯿﻨﻪ ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ در ﻗﻄﺮﻫﺎي ﻧﺴﺒﯽ ﺷﻤﻊ 0/6 و 0/9 ﺑﻪﺗﺮﺗﯿﺐ 50 و 60 درﺻﺪ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ. در ﺷﺮاﯾﻂ ﮐﺎرﮔﺬاري ﺳﺮﺷﻤﻊﻫﺎ ﻫﻢﺗﺮاز ﺑﺴﺘﺮ و ﻣﺪﻓﻮن، ﺗﻐﯿﯿﺮ آراﯾﺶ و ﻗﻄﺮ ﺷﻤﻊﻫﺎ، ﺗﺄﺛﯿﺮ ﻣﺤﺴﻮﺳﯽ ﺑﺮ ﺑﯿﺸﯿﻨﻪ ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ ﻧﺪاﺷﺖ. ﺑﺮرﺳﯽ ﻧﺘﺎﯾﺞ ﻣﺮﺑﻮط ﺑﻪ ﺿﺨﺎﻣﺖ ﺳﺮﺷﻤﻊ ﺣﺎﮐﯽ از آناﺳﺖﮐﻪ ﺑﺮاي ﺗﺮازﻫﺎي ﻧﺴﺒﯽ ﮐﺎرﮔﺬاري ﺳﺮ ﺷﻤﻊ ﺑﺎﻻي ﺑﺴﺘﺮ، ﺑﺎ اﻓﺰاﯾﺶ ﺿﺨﺎﻣﺖ ﻧﺴﺒﯽ ﺳﺮﺷﻤﻊ از 0/9 ﺑﻪ 1/4، ﻣﻘﺪار ﺑﯿﺸﯿﻨﻪ ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ ﺑﺮاي ﻫﻨﺪﺳﻪ و ﻗﻄﺮﻫﺎي ﻣﺨﺘﻠﻒ ﺷﻤﻊ، ﺑﻪﻃﻮر ﻣﺘﻮﺳﻂ 20 درﺻﺪ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ. ﻫﻢﭼﻨﯿﻦ ﺑﺎ اﻓﺰاﯾﺶ ﻗﻄﺮ ﺷﻤﻊﻫﺎ از 0/6 ﺑﻪ 0/9 در ﺗﺮازﻫﺎي ﻧﺴﺒﯽ ﮐﺎرﮔﺬاري ﺳﺮﺷﻤﻊ ﺑﺎﻻي ﺑﺴﺘﺮ، ﻣﻘﺪار ﺑﯿﺸﯿﻨﻪ ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ در آراﯾﺶﻫﺎي ﺷﻤﻊ 2×2 و 2×3، ﺑﻪﻃﻮر ﻣﺘﻮﺳﻂ 5 و 10 درﺻﺪ اﻓﺰاﯾﺶ ﯾﺎﻓﺖ.

In this research, the effects of pile cap thickness and its top level of installation, arrangement and diameter of piles on variation of local scour around the inclined bridge piers group were investigated experimentally. A Physical model of piers group having two inclined rectangular piers with 28 degrees inclination angle was constructed on a pile cap. Experiments were performed on piles group with relative diameters ( ) of 0.6 and 0.9, piles arrangement of 2×2 and 2×3, relative pile cap thicknesses ( ) of 0.9 and 1.4 and the pile cap relative installation levels ( ) of 1.5, 1, 0.5, 0 and also its buried condition at the level of -0.7 and -1.2. Comparison of the maximum scour depth indicated that the change of pile arrangement from 2×2 to 2×3 caused 50 and 60 percent increases in the scour depth related to the ratio of with the amount of 0.6 ad 0.9, respectively. However, changes of the pile diameter and arrangement did not have any effect on the maximum scour depth as pile cap installed in the same level of bed or lower than it i.e. in buried condition. Comparison of the results showed that changes of the pile cap thickness from 0.9 to 1.4 times the pier width, caused the maximum scour depth for all pile geometry and top level installation of the pile cap to be increased 20 percent approximately. Furthermore, as pile diameter increased from 0.6 to 0.9 bridge pier width, the maximum scour depth for installation of the pile cap above the bed increased 5 and 10 percent approximately for pile arrangement of 2×2 and 2×3, respectively.