بررسی تاثیر اندازه ذرات تشکیل دهنده فیوز پلاگ خاکی بر چگونگی شسته شدن آن

رایج‌ترین علت شکست سدها، به ویژه سدهای خاکی، روگذری جریان از تاج سد می‌باشد که ممکن است با تلفات جانی و خسارت‌های مالی زیاد همراه باشد. فیوز پلاگ به عنوان سوپاپ اطمینان برای محافظت از سد در برابر خرابی‌های فاجعه بار ناشی از روگذری جریان آب بکار می‌رود. در این تحقیق آزمایشگاهی، به بررسی نحوه تخریب فیوز پلاگ و دبی خروجی از مخزن سد، ناشی از تغییر اندازه ذرات تشکیل دهنده بدنه فیوز پلاگ پرداخته شده است. نکته حائز اهمیت در این تحقیق برای مشابهت هر چه بیشتر این فرآیند با واقعیت، ثابت نگه داشتن تراز آب در بالادست سازه در طول مدت روگذری جریان و تخریب سازه می‌باشد. بررسی توسعه و تکامل تدریجی شکاف، فرآیند و نرخ فرسایش و هیدروگراف خروجی حاصل از روگذری جریان ناشی از تغییر اندازه ذرات تشکیل دهنده بدنه، از نتایج این مطالعه آزمایشگاهی می‌باشد. طبق نتایج به دست آمده، در d* ( نسبت قطر متوسط ذرات به ارتفاع فیوز پلاگ) برابر با 0/004 بیشترین مقدار نرخ متوسط تخریب نسبت به دو d* دیگر یعنی 0/00133 و 0/006 رخ می دهد در d* برابر با 0/00133 نرخ خروج آب از فیوز پلاگ در حین تخریب و میزان h*، به ترتیب 2/25 درصد و 2/8 درصد بیش از دو d* دیگر است از سویی دیگر هر چه مقدار d* بزرگتر شود، اول آنکه خاکریز بیشتر حالت زهکش به خود گرفته و حجم آب مفید درون مخزن سد را بیشتر هدر می دهد و دوم آن که از پایداری خاکریز به دلیل رگاب احتمالی کاسته می شود با توجه به مجموعه دلایل ذکر شده d* معادل 0/004 مناسب ترین d* برای ساخت فیوز پلاگ در محدوده پارامترهای مورد آزمایش است.

investigating the effect of grain size of embankment fuse plug body on their washout mechanism

one of the main causes of damage to dams, especially earth dams is the overtopping which may cause huge human losses and financial damages. fuse plug is used as a safety valve to protect dams against catastrophic damages of overtopping. the increasing outbreak of floods and their huge and sometimes irrecoverable damages has incentivized dam experts and designers for more studies on the most effective and economical spillway construction. the attempt is towards letting higher amounts of water run through spillways. one approach is using an auxiliary spillway beside the main spillway. fuse plug can be used as an economical auxiliary or emergency spillway. fuse plug structure consist of embankment body and pilot channel. fuse plugs are designed with the same details and ingredients of many earth and rockfill dams. in terms of the material of their body, fuse plugs are categorized as either homogeneous or non-homogeneous. as a result of the embankment erosion, the waterway opens up. when the flood is over, the embankment is reconstructed. the fuse plug operation is totally automatic and does not require human intervention. at other times, fuse plug should be stable and have reliability coefficients equal to those of earth dams. in this experimental research, the effect of the body grain size of embankment fuse plug on the failure and washout mechanism of non-cohesive homogeneous fuse plug is evaluated. the water level upstream of fuse plug is kept constant throughout the overtopping and failure processes, the tests thereby simulating the failure of embankment fuse plug impounding a very large upstream reservoir. the failure trend and mechanism, rate of embankment sediment washout and the output hydrograph of overtopping are addressed. the breach shape and failure mechanism can be used as a guide to interpret the extent of grain size effect and failure progress. the mechanisms of embankment breach due to overtopping can be categorized into 2d and 3d processes. 3d mechanism consists of both lateral and vertical erosions, whereas 2d mechanism only consists of vertical erosion. in this research, both types of erosions were observed. initially 3d mechanism is observed and breach expansion continued until the breach reached the flume walls. then after the 2d mechanism failure was observed. also the equation obtained for describing non-dimensional embankment crest in 2d process by non-dimensional time and non-dimensional grain size. the mean rate of washout in test no.2 is the highest and an analysis similar to the mean rate of washout materials can be generalized to the washout period, which given the uniformity of the total volume of materials, is a rational generalization. the important point in the optimal performance of the fuse plug during the time of destruction is the volume of more outlet water in a shorter time period at the level desired by the designer. the material used in the embankment body with d* equal to 0.004, taking into account the results obtained, including the minimum water level behind the structure, reducing drained water, preventing structural instability due to the piping and the higher total erosion rate is an appropriate choice for building an embankment plug fuse in the range of test parameters.