بررسی پدیده رسوب شویی تحت جریان مستغرق در تخلیه رسوبات بالادست سدها با استفاده از مدل فیزیکی

در روش رسوب شویی تحت جریان مستغرق، مقدار حجم رسوبات تخلیه شونده به پارامترهای مختلفی بستگی دارد که می توان به عمق آب داخل مخزن، عمق آب داخل حوضچه، دبی جریان خروجی از تخلیه کننده تحتانی، اندازه و نوع رسوبات تجمع یافته در داخل مخزن اشاره نمود. برای بررسی پارامترهای مذکور در این پژوهش یک مدل فیزیکی به طول1 متر، عرض 1 متر و ارتفاع 1.1 متر و با اجرای آزمایش های مختلف با استفاده از 2 ارتفاع آب داخل مخزن ، 3 ارتفاع آب داخل حوضچه و با 3 نوع دانه بندی رسوب (در مجموع 81 آزمایش) استفاده گردید.نتایج این تحقیق نشان داد که در رسوب شویی تحت فشار زمانی که تخلیه کننده تحتانی برای رسوب شویی باز گردد، جلوی آنیک مخروط رسوب شویی تشکیل می شود. ابعاد مخروط رسوب شویی تشکیل شده به دبی خروجی از تخلیه کننده تحتانی، ارتفاع آب داخل مخزن و قطر رسوبات تجمع یافته در داخل مخزن بستگی دارد به طوریکه ثابت نگهداشتن ارتفاع آب مستغرق و افزایش ارتفاع آب داخل مخزن، موجب افزایش حجم و طول مخروط رسوب شویی می گردد. همچنین به ازای یک ارتفاع آب ثابت در داخل مخزن، افزایش ارتفاع آب مستغرق موجب افزایش میزان حجم و طول مخروط رسوب شویی می شود. نتایج نشان داد با افزایش 50 درصدی ارتفاع آب داخل مخزن به ازای ارتفاع آب ثابت داخل حوضچه، میزان آب شستگی نیز افزایش تقریبی 50 درصدی خواهد داشت. همچنین به ازای افزایش 66 درصدی ارتفاع آب داخلحوضچه، میزان آب شستگی به میزان تقریبی 19 درصد در حالت مخزن نیمه پر و 35 درصد در حالت مخزن پُر کاهش یافت. این افزایش وکاهش برای هر سه نمونه خاک مورداستفاده در آزمایش ها مشاهده گردید.

investigation the phenomenon of sediment flushing under submerged condition in the upstream of dams using physical model

introduction today, the most serious risk for the early death of dams is the risk of sedimentation of their reservoirs. among the conventional methods in thefield of sediment management in reservoirs of dams, we can refer to damming, construction of short dams upstream, dredging and flushing.since flushing is one of the most important and cheapest methods of recovering the lost volume of the tank, therefore, the investigation of thisphenomenon and the investigation of various parameters on it, as well as the investigation of its feasibility, have been of interest to researchersand engineers. hydraulic sediment washing is called a method in which by opening the lower drains of the bottom or a lower number, it is used to cause erosion of erodible sediments that have already been deposited inside the tank, this method is done in two ways:1- free hydraulic sediment washing, in this method, the water level of the tank is lowered by the bottom dischargers until the river flow takes place in the tank.2-hydraulic sediment washing under pressure, in this method, during sediment washing, the lower drains of the dam are usually opened for a certain period of time.methodology to check the mentioned parameters in this research, a physical model with a length of 1 meter, a width of 1 meter and a height of 1.10 metersand by performing various tests using 2 water heights inside the tank, 3 water heights inside the pond and with 3 types of sediment granulation (in total 81 experiments) were investigated and studied. in the research process, after data collection, the next step involves data analysis. data analysis is not only in a statistical way and there are many researches that lack statistical aspects and mainly rely on documents and rational perception and analysis. such research also follows the complete process of scientific research and has an analysis stage. therefore, analysis is generally of two types: quantitative analysis and qualitative analysis.some have classified quantitative analysis into descriptive analysis and explanatory (causal) analysis. at the level of descriptive quantitative analysis, the distribution of experimental data of each of the independent and dependent variables is expressed through appropriate statistical indicators.at the level of explanatory analysis, we are dealing with causal analysis, and the causal relationship between variables is sought. qualitative analysis can be done at three levels: description, explanation and interpretation. in carrying out the model tests, various options that are desired by the designer are studied and the values of scour holes are measured in each of them.in fact, the experiments were carried out both quantitatively and qualitatively, and when necessary, photographs were taken of the steps. each test was recorded in order to obtain more accurate results.in order to process the results easily and quickly, it is better that the process and steps of measurement are the same for all experiments and in a repetitive manner, so that while increasing the speed of the measurement, the error can be reduced as much as possible.