نوع مقاله : مقاله پژوهشی
نویسندگان
چکیده
در این مقاله تأثیر زاویه و ابعاد زهکش پنجه‌ای بر خط نشت آزاد آب در بدنه سدهای خاکی همگن با استفاده از مدل نرم آزمایشگاهی بررسی شده است. با توجه به خلأ مطالعاتی در مورد ارتفاع بهینه زهکش پنجه‌ای سدهای خاکی و عدم وجود استاندارد معروف و ملزوم، در این پژوهش به این موضوع مهم پرداخته و روش کار بحث شده است. بدین منظور مدل آزمایشگاهی مناسبی ایجاد شد. آزمایش‌ها با ارتفاع‌های مختلف آب در پشت دیواره سد خاکی همگن انجام شد و با استفاده از داده‌های پیزومتریک، وضعیت خط نشت آزاد آب در حالت‌های مختلف زهکش پنجه‌ای مقایسه شد. در پنجه سد سه نوع زهکش با زاویه‌های 45، 60 و 90 درجه در ارتفاعات مختلف ساخته شدند و روند خط نشت در بدنه سد خاکی در حالت‌های مختلف آزمایش و در حداکثر ارتفاع آب سد خاکی با استفاده از هفت چاهک مشاهداتی در بدنه سد و 30 پیزومتر در دیواره فلوم برداشت شد. زهکش‌ها در سه مقطع با سه ارتفاع ساخته شدند که در ادامه 9 مدل آزمایشگاهی آماده شد و داده‌های نشت و دبی برداشت گردیده شد. منحنی‌های برداشت شده در نقاط انتهایی خط نشت از روند خطی تبعیت می‌کردند این امر موجب شد معادلات ریاضی خط نشت در انتهای بدنه سد و ابتدای ورود به زهکش ترسیم گردد. و محل برخورد خط با بدنه زهکش از حل عددی معادلات ریاضی خط نشت و خط ریاضی در یک
کلیدواژه‌ها
عنوان مقاله [English]
Determination of the optimum size of a toe drain based on the best phreatic line in homogeneous earth dams by using vitro model
نویسندگان [English]
- saeed salehi
- mohammad shayannejad
- Seyed Saeed Okhravi
- navideh najafpour
چکیده [English]
In this study, first an earth dam was embanked homogeneously in a laboratory flume with 6 m length, 60 cm width and height of 1 m. The physical model was constructed with a height of 1 m and a length of 4.5 m in the foundation. The upstream and downstream slopes of the earth dam were (2.5-1), which are conventional slopes in a homogenous earth dam. In order to check and obtain the hydraulic conductivity in the range of the homogenous earth dam, two kinds of soil were blended and finally K was compared with the references. The obtained K was equal to 4 meters per day, which conform to previous studies. Afterwards, the effect of the angle and dimensions of the toe drain on the phreatic line was investigated in the homogenous dams. Lack of enough studies about the optimal size of toe drain and its applied standard is the main aim of this new research; that is why the applied lab model was constructed at Shahrekord University. First, the model was embanked from homogenous material and the data were collected from this model with and without toe drain in 3 situations. In every situation, 3 toe drains were used whose sizes were variable. To plot the seepage line, 30 piezometers were set up and their heads were measured. In addition, observation wells were dug in the body of the model. Therefore, the observation wells and piezometers were used to monitor the phreatic line. After that, the obtained results were compared with each other using the Excel software and the tolerance was calculated. Eventually, the 10 situations were plotted. One of them had no toe drain and 9 of them had a toe drain. For example, in the first experiment, a toe drain with an angle of 45 degrees was used. Subsequently, the other toe drains angles were also examined. For solving the problem of dimension used (p/h) index that p was the height of the drain and h was height of water in reservoir of earth dam. Location of data sampling had been at behind of the homogenous earth dam wall on different height of water. Height of water fixed in 3 states in physical model (30, 60 and 80 centimeter). In state one and state two the phreatic line never coincide the downstream side of the earth dam body. Finally, it has decided to use the data of 80 centimeters. Situation of phreatic line will be monitored by using piezometers installed in different locations of toe drain. Three types of drain with constant angle (45, 60 and 90 degree) were instructed at different heights and the phreatic line was monitored for different experiments on the homogenous earth dam at maximum height of water. The best formation and dimension of stony toe drain is gotten by collation of different equations on phreatic line (based on comparison by experiment without drain). The results showed that the homogenous earth dams can be obtained highest loss in phreatic line when upward of toe drain angle and its top height had 45 degrees and 0.35 maximum height of water in the reservoir. Also in 90 degree toe drain the effect of toe drain on seepage was very well. It means that this toe drain have much head loss in seepage line, but the defect of this mater shown in this way when the toe drain created with big size (p/h= 0.35) and (90 degree) the flux of seepage was too much. So for a solution for this problem was using a form of toe drain which have a perfect head loss in seepage line and have optimum flux that exit in the toe drain that constructed in down slope of the dam. If it decided to show the effect of another toe drain like (p/h=0.35 and 60 degrees) this case, the toe drain with 90 degree has more flux than toe drain with 45 degree, but it hasn’t optimum head loss. Finally, by comparing all of states, the best toe drain that has the optimum loss head and seepage flux was introduced.In this study, first an earth dam was embanked homogeneously in a laboratory flume with 6 m length, 60 cm width and height of 1 m. The physical model was constructed with a height of 1 m and a length of 4.5 m in the foundation. The upstream and downstream slopes of the earth dam were (2.5-1), which are conventional slopes in a homogenous earth dam. In order to check and obtain the hydraulic conductivity in the range of the homogenous earth dam, two kinds of soil were blended and finally K was compared with the references. The obtained
کلیدواژه‌ها [English]
- piezometer
- toe drain angle
- homogenous earth dams
- toe drain length
- phreatic line
- toe drain height
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