بررسی آزمایشگاهی آبشستگی اطراف پایه پل با دماغه مایل

محورهای موضوعی : برگرفته از پایان نامه

محسن سلیمانی بابرصاد ^{1 *} , عباس صفائی ²

1 - گروه مهندسی آب، مرکز تحقیقات علوم آب و محیط زیست، واحد شوشتر، دانشگاه آزاد اسلامی، شوشتر، ایران.
2 - عضو مرکز تحقیقات علوم آب و محیط زیست، واحد شوشتر، دانشگاه آزاد اسلامی، شوشتر، ایران.

تاریخ دریافت : 1398/06/19 تاریخ پذیرش : 1400/02/06 تاریخ انتشار : 1400/02/01

کلید واژه: آبشستگی, پایه پل, زاویه دماغه, آستانه حرکت,

چکیده مقاله :

مقدمه و هدف: اصلی‌ترین عامل تخریب پایه پل‌ها، آبشستگی موضعی اطراف آنها می‌باشد. جهت کنترل این پدیده،‌ مطالعات بسیاری انجام شده، و راهکارهایی جهت حفاظت از پایه پل‌ها ارائه گردیده است. راهکارهای حفاظت از پایه‎های پل به دو روش مستقیم و غیرمستقیم تقسیم می‌گردند، یکی از روش‌هایی که بصورت غیرمستقیم با کمک اصلاح خطوط جریان اطراف پایه پل، می‌تواند عمق آبشستگی را کاهش دهد تغییر زاویه دماغه پل می‌باشد.
مواد و روش­ها: در این تحقیق بصورت آزمایشگاهی به بررسی تاثیر تغییر زاویه دماغه پایه پل با راستای جریان پرداخته شد. از این رو زاویه راستای برخورد جریان با دماغه پایه (α) 90 ، 85، 80، 75 و 70 درجه در شرایط آب زلال مورد بررسی قرار گرفت. در تمامی آزمایش‌ها عمق آب 10 سانتیمتر، قطر متوسط ذرات D₅₀=0.95 mm و جهت بررسی اثر هیدرولیک جریان، سرعت‌های نسبی متفاوت در نظر گرفته شد.
یافته­ها: در بهترین حالت، پایه پل با زاویه برخورد 70 درجه توانست، در سرعت‎های کمتر از 60 درصد سرعت آستانه حرکت ذرات، 95 درصد و در سرعت‌های تا 95 درصد سرعت آستانه حرکت ذرات، به طور متوسط 36 درصد عمق آبشستگی را نسبت به پایه شاهد کاهش دهد.
بحث و نتیجه­گیری: با کاهش زاویه برخورد جریان با پایه به دلیل انحراف بخشی از خطوط جریان و عدم چرخش آنها به سمت بستر، باعث می‌گردد پتانسیل منطقه پرفشاری که در حالت پایه شاهد ایجاد گردیده، نسبت به حالتی که زاویه دماغه کاهش می‌یابد تقلیل یابد، و باعث کمتر شدن توان جریان پایین رونده و به سبب آن ضعیف شدن توان جریان‌های نعل اسبی، که عامل اصلی توسعه حفره آبشستگی هستند، ‌گردد.

چکیده انگلیسی:

Introduction:The leading cause of damages on bridge is local scouring around piers. Many studies were carried out to control and reduce this phenomenon and suggested more solution methods to protect bridge piers. Protection is divided into direct and indirect methods. In this study, to reduce scouring depth around the pier, an indirect method is used by changing the pier's head angle in a flow direction.
Materials and Methods:An experimental study on clear-water at a different angle of piers head under steady flow is presented. Experiments were used to assess the ability to change the head angle of piers to protect them. Toward this end, five angles (α) 90, 85, 80, 75, 70-degree with the flow direction were considered. The bed material size d₅₀ was 0.9 mm and all experiments were done in Gunt hydraulic standard flume.
Findings:The results showed that the pier with a 70-degree attack angle could reduce the scour depth more than others. This happens due to diverting part of streamlines to downstream, and it can have a 36 per cent reduction overall.
Conclusion:The scouring depth and sediment point bar created around the pier with an inclined head compared with the control pier (α=90-degrees) have less scouring depth due to minor deviation of flow streamlines and reduction of disturbances around the pier.

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