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標題: 鋼製梳子壩之囚砂與排砂效益
Sediment trapping and removing efficiency by slit check dam with steel
作者: 魯聲睿
Lu, Sheng-Jui
Contributors: 陳樹群
水土保持學系所
關鍵字: 鋼製梳子壩;混凝土梳子壩;可拆卸式橫桿;排砂
Slit check dam with steel;slit check dam;removable transverse beam;sediment removal
日期: 2013
Issue Date: 2013-11-07 13:16:08 (UTC+8)
Publisher: 水土保持學系所
摘要: 臺灣傳統之土石流防治工法,以全封閉式壩與混凝土梳子壩為主;然而,全封閉式壩無選擇性攔阻泥砂,在臺灣河川之河床質與懸浮載皆高的環境條件下,往往一兩場暴雨過後便淤滿,失去其攔阻泥砂之功能。混凝土梳子壩為透過性壩體,雖可避免在短時間內淤積過量,可是在同為土石流發生頻繁的日本,在近年研究中卻發現,其因迴水或溪床坡度過緩而提前堆積之淤積模式,可能導致後續水流挾帶大量土石一併越過壩體,對下游所欲保護之對象造成災害。因此,本研究以近年較新式之土石流防治工法—鋼製結構物,利用會呼吸的防砂壩之概念,在其上裝置可拆卸式的橫向功能部材,並利用水工實驗渠道來進行實驗。
本研究在惠蓀林場蘭島溪二號橋,即實體鋼構壩設置地點,進行表面粒徑調查,並利用幾何相似定律進行模型及礫石之縮比,以符合室內實驗渠槽之大小。本研究著重在混凝土梳子壩與鋼製梳子壩,在囚砂與出砂時型態之差異,以及於出砂速率、出砂量與貯砂率上之比較。並在不同拆除方式下,觀察鋼製梳子壩排砂形式之異同,以及於排砂速率、排砂率、粒徑分佈上之差別。實驗結果發現,在小流量和大流量時,鋼製與混凝土梳子壩的貯砂率與總出砂量差距較大,分別是由於通水斷面積之差異與大流量時溢流的作用。在裝置橫桿後,鋼製與混凝土梳子壩都能有效降低出砂速率、總出砂量、以及提升囚砂之效益;此外,土石流洪峰之出砂量,是隨橫桿純間距縮小而減少的。
本研究依實驗結果,提出以下觀點:(1) 鋼製與混凝土梳子壩皆能將巨大礫石攔阻下來,並藉由礫石間互相卡合,將土石流整體停止下來;除此之外,鋼製梳子壩還能排出更多的細顆粒,以補充下游河川所需之泥砂。(2) 鋼製梳子壩在裝置橫桿後,其攔阻礫石之效果與混凝土梳子壩是相當地;因此,若在生態保育需要上,且利於維護管理的地方,可考慮使用鋼製梳子壩來代替混凝土梳子壩。(3) 影響堆積體排砂的因素,為最下方通口斷面之高度,其同時也控制了排砂速率的快慢;因此,在排砂階段時,應視集水區內土砂安定之程度,來決定橫桿拆除之根數與壩體拆除的程度。
The traditional debris flow control engineering in Taiwan is using of close check dam and slit check dam. Nevertheless, environment conditions of Taiwan’s river are high in bed load and suspension load both, hence close check dam which trap all kind of sand or slit is usually full and losing its ability of trapping after few storms. Slit check dam is permeable dam, so it can prevent from depositing all of sand or slit coming from upstream river in non-flood period. However, in recent years, Japan’s research showed that slit check dam of mode of deposit causing by backwater or lower channel slope may result in massive rocks crossing over the dam. As a result, slit check dam with steel and removable transverse beams new debris flow control engineering and the concept of dam of respiration were used to execute experiments in indoor channel.
Particle size distribution test of surface was executed at Lan-Dow river, and used the laws of geometric similitude to design model of dam and experimental rocks. The main comparisons focused on types of sediment trapping and removing, rate of sediment discharge, sediment discharge, and trapping rate between slit check dam and slit check dam with steel. In different types of removing transverse beam showed different kind of sediment removal of slit check dam with steel and differences on rate of sediment removing, removing rate, and particle size distribution. The result of experiment showed that trapping rate and total sediment discharge had more difference between slit check dam and slit check dam with steel on low and high flow rate, because of difference of water area and effect of overflow respectively. Slit check dam and slit check dam with steel could reduce rate of sediment discharge and total sediment discharge, and improve sediment trapping efficiency after installing transverse beams. Furthermore, sediment discharge of peak of debris flow was lower when net distance of transverse beam was smaller.
Conclusion of result of experiment: (1)Slit check dam and slit check dam with steel could trap most giant rocks both and stop debris flow by locking between rocks. In addition, slit check dam with steel could also discharge more fine sediment to supply the need of downstream river. (2)The efficiency of sediment trapping in slit check dam with steel after installing transverse beams was equal to slit check dam. Therefore, slit check dam with steel could instead of slit check dam if there had the requirement of ecological conservation and was easy to maintain and manage. (3)The factor of sediment removing was affected by height of bottom of water area, which also controlled the rate of sediment removing. Consequently, decision of the number of removing transverse beams and step of dam removal should in accordance with degree of stability of sediment in watershed in period of sediment removal.
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