بررسی آزمایشگاهی آبشستگی پیرامون ترکیب‌های مختلف آبشکن‌های سری نفوذناپذیر

اصلاح مسیر رودخانه به‌منظور کنترل سیلاب، جلوگیری از فرسایش بستر، تثبیت و حفاظت دیواره‌ها و همچنین تنظیم عرض رودخانه از جمله اهدافی هستند که در استفاده از آبشکن در نظر گرفته می‌شود. آبشکن‌های متداول دارای شکل‌های هندسی ساده، l و t هستند. این پژوهش در راستای بهینه کردن ترکیب‌های مختلف آبشکن‌های سری در جهت کاهش آبشستگی انجام شده‌است. آبشکن‌های نفوذناپذیر با اشکال هندسی مختلف به‌صورت سری 3 تایی در ترکیب‌های متفاوت تحت شرایط u/ucr≈0.95 مورد بررسی آزمایشگاهی قرار گرفتند. آبشکن اول در همه ترکیب‌ها t شکل بوده است. نتایج نشان داد برای آبشکن اول، در 10% زمان تعادل، بیش از 90% آبشستگی نهایی اتفاق می‌افتد. بهترین حالت از نظر متوسط عمق آبشستگی در هر سه موقعیت، ترکیب (t l t) است که در حدود 1/4 برابر عمق جریان فرسایش دارد. همچنین از دیدگاهی دیگر بهترین عملکرد در کل محدوده مورد حفاظت آبشکن‌ها با توجه به حجم فرسایش مربوط به ترکیب (t i i)می‌باشد که دارای حداقل حجم آبشستگی در حدود 70% بیشترین حجم فرسایش در ترکیب‌های دیگر است. پس در طراحی باید بهترین حالت با در نظر گرفتن اهداف برای بهره‌برداری و بهینه استفاده شود.

experimental investigation of scouring around different combinations of impermeable series spur dikes

improvement of the river route is one of the goals that considered in using a spur dike to control the flood, prevent bed erosion, stabilize and protect the walls, and set river width. spur dikes are structures that with adjustment hydraulic conditions and make smooth flow cause to reduce flow erosion power and the ability to carry sediments. and also makes good situations for sedimentation and sides consolidation. spur dikes are permeable and impermeable. impermeable spur dikes have different shapes which according to erosion amount and condition can be used. common spur dikes have simple, l and t-shaped geometric shapes. this research has been conducted to optimize the various combinations of spur dikes to reduce scouring. all of the scour and flow measurements were collected in a flume with 14 m long, 1.5 m wide, and 0.6 m deep located at the soil conservation and watershed management research institute. impermeable spur dike with different geometric shapes were tested in a series with 3 spur dikes for different compositions in u/ucr≈1 conditions. due to threshold flow condition by using shields parameters in all tests, the calculated discharge at the mentioned conditions is 28.5 lit/s. so according to discharge and flume dimensions in all the experiments, thereby concentrating on clear-water scour condition, flow depth (y) was taken as 0.06 m. for determine the equilibrium scour depth for each geometric, control test with 30 hours have been done. the first spur dike in all combinations was t-shaped. the results show that for first spur dike in combinations, in 10% of scouring equilibrium time, about 90% of scouring occurred. so with these results, 300 min (5 hours) test time was selected for do all main tests to achieve more than 85% of scouring. also, in the results of different tests it was observed that maximum scour depth happens around first spur dike. so geometry of first spur dike is very important in reduce average scour depth in combinations. mean scour depth in these combinations for first, second and third position respectively are about 2.44y, 1.21y and 0.75y which in that for second and third positions with 50% and 69% have fewer scour depth in comparison with first position. combination (t l t) is the best composition for the lowest average scour depth in all three positions, which 2 times the flow depth have erosion. the best performance in the whole range of spur dikes due to the amount of erosion volume is for the composition (t i i), that’s about 70% of the massive erosion in other compositions. mean scour depth in all positions for these 2 series are 1.39y and 1.63y. average scour depth in (t t t) series is 1.41y which more than (t l t) combination. the reason for this results can be effect of middle l-shaped spur dike on t-shaped spur dike scour depth in third position. this effect cause to reduce scouring in about 28%. (t i i), (t l t) and (t t t) series spur dikes are the best combinations which each one has special performance, therefore, for design, the best composition should be choice for target of exploitation and optimal economic conditions.