تعيين عمق و ابعاد بهينه المان هاي زبري بر روي تكيه گاه پل براي كاهش ميزان آبشستگي

Determination of Optimum Depth and Dimensions of Roughening Elements on Bridge Abutment as Scour Countermeasures

ﺳﺎلﻫﺎي اﺧﯿﺮ دﻟﯿﻞ ﺗﺨﺮﯾﺐ ﺑﺴﯿﺎري از ﭘﻞﻫﺎ آﺑﺸﺴﺘﮕﯽ ﺗﮑﯿﻪﮔﺎه اﻋﻼم ﺷﺪه اﺳﺖ. ﺗﺤﻘﯿﻘﺎت ﺑﺴﯿﺎري ﺑﻪ ﮐﻢ ﮐﺮدن آﺑﺸﺴﺘﮕﯽ ﺗﮑﯿﻪﮔﺎه ﺑﻪ ﮐﻤﮏ ﺳﺎزهﻫﺎﯾﯽ ﮐﻪ اﺛﺮ ﺗﺨﺮﯾﺒﯽ ﺟﺮﯾﺎن را ﺑﻬﺒﻮد ﻣﯽﺑﺨﺸﻨﺪ ﭘﺮداﺧﺘﻪاﻧﺪ. در اﯾﻦ ﻣﻄﺎﻟﻌﻪ ﺑﻪ ﺑﺮرﺳﯽ آﺑﺸﺴﺘﮕﯽ آب زﻻل در دو ﺗﮑﯿﻪﮔﺎه ﻋﻤﻮدي ﺑﺎ ﻋﺮضﻫﺎي ﻣﺨﺘﻠﻒ ﭘﺮداﺧﺘﻪ ﺷﺪه اﺳﺖ. دﯾﻮارهي ﺑﺎﻻدﺳﺖ ﺗﮑﯿﻪﮔﺎه ﺑﺎ اﻟﻤﺎنﻫﺎﯾﯽ ﺑﺮاي ﮐﺎﻫﺶ ﮔﺮداﺑﻪﻫﺎي ﻧﻌﻞ اﺳﺒﯽ ﻣﺤﺎﻓﻈﺖ ﺷﺪه اﺳﺖ. اﻧﺪازهﻫﺎي ﻣﺨﺘﻠﻒ اﻟﻤﺎنﻫﺎ ﺑﺎ ﺿﺨﺎﻣﺖ و ﭘﯿﺶآﻣﺪﮔﯽ ﺑﺮاﺑﺮ ﺑﺎ 0/05L ،0/025L، L) 0/3L ،0/2L ،0/1L ﺑﺮاﺑﺮ ﺑﺎ ﻃﻮل ﺗﮑﯿﻪﮔﺎه( و در ارﺗﻔﺎعﻫﺎي ﻣﺨﺘﻠﻒ ﮐﺎرﮔﺬاري ﺑﺮ دو ﺗﮑﯿﻪﮔﺎه ﺑﺎ ﻃﻮل ﺑﺮاﺑﺮ و ﻋﺮض ﯾﮑﯽ دو ﺑﺮاﺑﺮ دﯾﮕﺮي ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار ﮔﺮﻓﺘﻪاﻧﺪ. ارﺗﻔﺎع ﺑﻬﯿﻨﻪ اﻋﻤﺎل زﺑﺮي، ﺑﺮاﺑﺮ ﺑﺎ 0/6L زﯾﺮ ﺳﻄﺢ رﺳﻮب ﺑﻪ دﺳﺖ آﻣﺪ. ﺑﺎ ﺑﺰرﮔﺘﺮ ﺷﺪن اﺑﻌﺎد اﻟﻤﺎنﻫﺎ ﺗﺎ ﺿﺨﺎﻣﺖ و ﭘﯿﺶآﻣﺪﮔﯽ 0/2L، آﺑﺸﺴﺘﮕﯽ اﻃﺮاف ﺗﮑﯿﻪﮔﺎه ﮐﻢ ﻣﯽﺷﻮد و ﭘﺲ از آن ﺑﺎ ﺑﺰرﮔﺘﺮ ﺷﺪن اﻟﻤﺎنﻫﺎ آﺑﺸﺴﺘﮕﯽ اﻓﺰاﯾﺶ ﭘﯿﺪا ﻣﯽﮐﻨﺪ. ﮐﺎرﮔﺬاري اﻟﻤﺎنﻫﺎي ﺑﺎ ﺿﺨﺎﻣﺖ و ﭘﯿﺶ آﻣﺪﮔﯽ 0/2L در ﻋﻤﻖ 0/6L زﯾﺮ رﺳﻮب ﺑﺮ ﺗﮑﯿﻪﮔﺎه ﺑﺎ ﻋﺮض ﮐﻤﺘﺮ، ﮐﺎﻫﺶ آﺑﺸﺴﺘﮕﯽ ﺑﻪ ﻣﯿﺰان 30/4 درﺻﺪ و ﺑﺮ ﺗﮑﯿﻪﮔﺎه ﺑﺎ ﻋﺮض ﺑﯿﺸﺘﺮ ﮐﺎﻫﺶ آﺑﺸﺴﺘﮕﯽ ﺑﻪ ﻣﯿﺰان 32/8 درﺻﺪ را ﻧﺘﯿﺠﻪ داد.

In the recent years, the failure of many bridges has reported due to local scour around abutment. Many studies have focused on reducing the scour with the help of structures reducing the destructive effects of flow. In this study, the scouring effect on two vertical wall abutments with different widths was investigated using clean water. Where the upstream face of the latter is protected with roughening elements as devices to intercept the down flow responsible for the formation of the principal vortex. Different sizes of the elements with thicknesses and protrusions equal to 0.025L, 0.05L, 0.1L, 0.2L and 0.3L (L is the length of the abutment) placed at different elevations on abutments were investigated. The optimum elevation of roughening elements obtained at 0.6L below the bed level. As the thickness and protrusion dimensions of the elements increases to 0.2L, scour depth around the abutment decreases, and after that increases if the element size become larger. In conclusion, the roughening elements with thickness and protrusion equal to 0.2L and placement of 0.6L below the sediment bed reduced the scour depth 30.4 and 32.8% at the small and large abutments, respectively.