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標題: 防砂壩下游帶工佈置之試驗研究
Experimental study of riverbed girdle arrangements in the downstream of Sabo dam
作者: 陳聖文
Chen, San-Wen
關鍵字: free over-fall flow
riverbed girdle
scour hole
出版社: 土木工程學系
摘要: 台灣防砂壩受損的原因大多由於投潭水流淘刷及毀壞下游保護工,進而影響壩基之穩定所造成。本研究利用前人對於堰壩投潭水流對於下游天然河床沖刷之相關研究,運用在堰壩下游縱向斷面鋪設不干擾流場之壓力量測系統,測定投潭水流下游段縱向渠床壓力變動分佈情形,設計出三種不同佈置尺度的帶工構造物(Riverbed Girdle),進行不同坡度下之投潭沖刷試驗。 研究結果發現帶工佈置能使泥砂沖刷體積量減小,並使沖刷坑位置較遠離壩址,而與無帶工佈置比較發現平均沖刷坑最大刷深量減小58%,沖刷坑面積、形狀因子比值分別為2.63、2.53 (即為狹長型沖刷坑)之關係。當渠床若有帶工佈置時,當水流沖擊帶工渠面將有減力與消能之定性,經與無帶工佈置者比較分析,獲致作用力衰弱約32∼35%及能量消減約為58%所致。惟當渠床坡度變陡時,投潭水流的沖刷潛能及沖擊力會變大,導致泥砂顆粒較易被水流起動沖刷,因而使得沖刷現象加劇。而就不同佈置工法而言,帶工佈置一、二因水墊區受到壩體與帶工間泥砂孔隙效應之影響,使其水流作用力會略小於設計方式類似護坦之帶工佈置三。依經濟成本效應與工法設計方便性之評估,帶工佈置一較符合工程上之需求。
Most hydraulic structures failures in Taiwan (such as the Sabo dam) were due to the scouring of downstream protective structures. The result of recent research on the local scouring of free over-fall flows are referenced in this study. A pressure transducer that has no effect on the flow filed was laid to measure the pressure distribution in the downstream channel. The three best riverbed girdles lengths for varied flow could then be proposed by reducing the pressure on the maximal pressure position. A scouring experiment for varied slopes was processed to determine scouring characteristics. In contra-position to the riverbed girdles, a scouring experiment without a riverbed girdle was also carried out. According to the experimental data, the scouring volume of the scouring hole decreased and scouring occurred farther from the Sabo dam. To compare the relationship between the scouring experiment without riverbed girdle the average maximum scouring depth decrease 58% was determined. The area of the scour hole and the shape factor were partitioned 2.63 and 2.53 times. (That is a slender scour hole). When the trench bed with the riverbed girdle dispose, the flow impact upon the riverbed girdle trench surface would have a coast-down force and qualitative energy dissipation, compared with the non riverbed girdle dispose, to obtain an action debility of about 32~35 percent and an energy decrease of 58 percent. When the trench bed gradient becomes steep, the potential impact of a free over-fall flow wash will wax, lead sediment particles to be washed away easily by the flow, thus causing the wash phenomenon to prick up. Riverbed girdles can be divided into types Ⅰ and Ⅱ because the circulation zone influences a small opening between the dam and riverbed girdles possess a flow action with a smaller design mode allied to type Ⅲriverbed girdles. For the economy cost and convenience of riverbed girdle design, type Ⅰ riverbed girdles will be more suitable for engineering requirements.
Appears in Collections:土木工程學系所



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