بررسي آزمايشگاهي تاثير برداشت مصالح در آبشستگي اطراف گروه پايه هاي مسلح شده

Experimental Investigation of the River Materials Mining Effect on the Scouring Around Armed Pier Groups

پديده آﺑﺸﺴﺘﮕﯽ اﻃﺮاف ﭘﺎﯾﻪﻫﺎي ﭘﻞ ﺑﻪ ﺧﺼﻮﺻﯿﺎت ﻫﯿﺪروﻟﯿﮑﯽ ﺟﺮﯾﺎن، ﺷﮑﻞ و ﻓﺎﺻﻠﻪ ﻗﺮارﮔﯿﺮي ﭘﺎﯾﻪﻫﺎ ﻧﺴﺒﺖ ﺑﻪ ﻫﻢ، ﺟﻨﺲ و اﻧﺪازه داﻧﻪﺑﻨﺪي ﺑﺴﺘﺮ رودﺧﺎﻧﻪﻫﺎ ﺑﺴﺘﮕﯽ دارد. ﻫﺪف از ﺗﺤﻘﯿﻖ ﺣﺎﺿﺮ ﺑﺮرﺳﯽ ﺗﺎﺛﯿﺮ ﮔﻮدال ﺣﺎﺻﻞ از ﺑﺮداﺷﺖ ﻣﺼﺎﻟﺢ در ﻣﯿﺰان آﺑﺸﺴﺘﮕﯽ اﻃﺮاف ﮔﺮوهﭘﺎﯾﻪﻫﺎ اﺳﺖ. ﺑﻨﺎﺑﺮاﯾﻦ ﺑﺮاي ﮐﺎﻫﺶ اﺛﺮ ﻣﻨﻔﯽ اﯾﻦ ﺑﺮداﺷﺖ، از ﮔﺮوهﭘﺎﯾﻪﻫﺎﯾﯽ ﺑﺎ دورﭘﯿﭻ ﮐﺎﺑﻞ ﺑﻪ ﻋﻨﻮان ﻣﺴﻠﺢﮐﻨﻨﺪه اﺳﺘﻔﺎده ﮔﺮدﯾﺪ. ﮔﺮوهﭘﺎﯾﻪﻫﺎ از ﺳﻪ ﭘﺎﯾﻪ ﻣﺘﻮاﻟﯽ در راﺳﺘﺎي ﺟﺮﯾﺎن ﺗﺸﮑﯿﻞ ﺷﺪهاﻧﺪ. آزﻣﺎﯾﺶﻫﺎ در دو ﺣﺎﻟﺖ ﺳﺎده و ﻣﺴﻠﺢﺷﺪه ) v ﺷﮑﻞ(، در ﺑﺴﺘﺮ ﻣﺎﺳﻪاي ﺑﺎ داﻧﻪﺑﻨﺪي 0/78 ﻣﯿﻠﯽﻣﺘﺮ ﺑﻪ ﻃﻮل 4/25 ﻣﺘﺮ، درون ﮐﺎﻧﺎﻟﯽ ﺑﻪ ﻃﻮل 13 ﻣﺘﺮ و ﻋﺮض 1/2 ﻣﺘﺮ اﻧﺠﺎم ﮔﺮﻓﺘﻪ اﺳﺖ. ﺗﺎﺛﯿﺮ ﺑﺮداﺷﺖ ﻣﺼﺎﻟﺢ ﺑﺮ ﻣﯿﺰان آﺑﺸﺴﺘﮕﯽ در ﻫﺮ دو ﻗﺴﻤﺖ ﺑﺎﻻدﺳﺖ و ﭘﺎﯾﯿﻦدﺳﺖ ﮔﺮوهﭘﺎﯾﻪﻫﺎي ﻣﺬﮐﻮر در ﺷﺮاﯾﻂ ﺟﺮﯾﺎن زﯾﺮ ﺑﺤﺮاﻧﯽ )ﻣﺤﺪوده ﻋﺪد ﻓﺮود 0/25 و 0/5( ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار ﮔﺮﻓﺖ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن داد ﮐﻪ در ﺗﻤﺎم آزﻣﺎﯾﺶﻫﺎ، ﺑﺮداﺷﺖ ﻣﺼﺎﻟﺢ از ﺑﺎﻻدﺳﺖ ﮔﺮوهﭘﺎﯾﻪ ﺑﺎﻋﺚ ﮐﺎﻫﺶ و ﺑﺮداﺷﺖ از ﭘﺎﯾﯿﻦدﺳﺖ ﮔﺮوهﭘﺎﯾﻪ، ﻣﻮﺟﺐ اﻓﺰاﯾﺶ ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ ﺑﯿﺸﯿﻨﻪ ﮔﺮدﯾﺪ. ﻫﻤﭽﻨﯿﻦ ﺑﺎ اﻓﺰاﯾﺶ ﻋﺪد ﻓﺮود از 0/25 ﺑﻪ 0/5، در ﺗﻤﺎم ﭘﺎﯾﻪﻫﺎ و ﺑﺮاي ﻫﺮ دو ﺑﺴﺘﺮ ﺑﺪون ﮔﻮدال )اﻟﻒ( و ﺑﺎ ﮔﻮدال )ب(، ﻋﻤﻖ آﺑﺸﺴﺘﮕﯽ اﻓﺰاﯾﺶ ﭼﺸﻢﮔﯿﺮي داﺷﺘﻪ اﺳﺖ. ﺑﻄﻮرﯾﮑﻪ ﮐﻤﺘﺮﯾﻦ اﻓﺰاﯾﺶ آﺑﺸﺴﺘﮕﯽ ﺑﺮاي ﺣﺎﻟﺖ )اﻟﻒ( و )ب( ﺑﻪ ﺗﺮﺗﯿﺐ ﺣﺪودا ﺑﺮاﺑﺮ 44 و 66 درﺻﺪ، ﻣﺮﺑﻮط ﺑﻪ ﭘﺎﯾﻪ آﺧﺮ از ﮔﺮوهﭘﺎﯾﻪ ﭘﺎﯾﯿﻦدﺳﺖ و ﺑﯿﺸﺘﺮﯾﻦ اﻓﺰاﯾﺶ آﺑﺸﺴﺘﮕﯽ ﺑﻪ ﺗﺮﺗﯿﺐ 75 و 76 درﺻﺪ در ﭘﺎﯾﻪ اول از ﮔﺮوهﭘﺎﯾﻪ ﺑﺎﻻدﺳﺖ ﻣﺸﺎﻫﺪه ﮔﺮدﯾﺪ.

The scouring phenomenon around the bridge piers depends on the hydraulic properties of the flow, shape, and spacing of the pier relative to each other, the material and grading of the rivers bed. The purpose of this study was to investigate the effect of cavity, caused by materials mining, on scouring around the pier groups. Therefore, in order to reduce the negative effect of this mining, pier groups armed with cable were used. Pier groups were performed of three consecutive piers in the direction of flow. The experiments were carried out in two simple and armed modes (v shape), in sand bed with a median grain size of 0.78 mm, with a length of 4.25 meters, in a canal with 13 meters in length and 1.2 meters in width. The effect of materials mining on scouring in upstream and downstream of the mentioned pier groups was investigated under subcritical flow conditions (range 0.25-0.5). The results showed that in all experiments, materials mining from the upstream of the pier group reduced the scour maximum depth, but mining from the downstream of the pier group increased the scour maximum depth. Also, with increasing the Fraud number from 0.25 to 0.5, the scour depth was significantly increased in all piers and for two beds; without a pithole bed (a) and with a pithole bed (b). So that the least increase in scouring for A and B conditions was about 44 and 66%, respectively for the last pier in downstream pier group and the most increase in scoring was observed to be 75 and 76%, respectively for the first pier in upstream pier group