Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/34064
標題: 平面透水柵對渠床沖刷及土石流防治之研究
A Study on Channel Bed Scour and Debris Flow Control by Bottom Infiltration Screen
作者: 張敬昌
關鍵字: 
出版社: 水土保持學系
摘要: 
中文摘要
西元1999年9月21日大地震後,臺灣地區土石流災害頻傳,且規模急遽擴大,防治工法雖不斷推陳出新,其中壩體型式中,非透過性壩與透過性壩仍為主要構造,兩者對於遭巨石撞擊問題為最大隱憂,另外,非透過性壩由於無選擇性攔阻,一旦淤滿,貯砂空間即喪失,當新一波土石流來襲時,僅能防止擴大土石流規模,未能有效降低其規模。縱觀臺灣1420條土石流潛勢溪流,存在為數甚多已淤滿非透過性壩,無法積極防治土石流,為活化其降低土石流規模之能力,研究將平面透水柵與其共構。
本論文利用室內水槽佈置,模擬上游河床坡度因淤積土砂而為原河床坡度2/3情形下,將防砂壩結合透水柵成為共構體,依據過壩水流沖刷機制及因次分析方法為基礎,以清水流沖刷共構體,探討溢壩水舌因平面透水柵影響對壩下游渠床沖刷機制,得出沖刷坑坑心距、坑深、坑長分別與渠床坡度、柵距、柵長、渠床平均粒徑、壩溢流口寬等因子無因次迴歸式,可解析其間互動消長規律,並深入瞭解對渠床減緩沖刷的功能;另以模擬土石流通過共構體,觀測其泥砂體積濃度與泥砂量的變化,輔以傳輸方程式及因次分析方法,解析泥砂體積濃度比與柵距、柵長間互動機制,並以統計方法建立其無因次迴歸關係式,最後探討平面透水柵在共構體中對土石流防治功效良窳。
經過1134次試驗證明,僅已淤積防砂壩對土石流泥砂體積濃度降低能力平均值不及5.7%,若能結合平面透水柵成為共構體來防治土石流,對泥砂體積降低能力平均值可提高至30.3%~56.8%,其中平面透水柵泥砂體積濃度降低能力平均值為僅設壩的5.7倍~8.9倍,在共構體中肩負 以上防治效率。
同時經試驗分析,得出沖刷機制或土石流防治效能表現中,平面透水柵的柵距大小,為主要影響因子,土石流通過共構體若 小於0.99時,共構體對土石流泥砂體積濃度降低能力能達25%以上。
由試驗印證,已淤積既設防砂壩下游結合平面透水柵後,由於平面透水柵分散水束與消能效果,壩下游沖刷坑坑深變淺,其坑深相對折減率普遍小於零,坑心距也遠離壩體,其坑心距位移率普遍大於零,坑長拉長,其形狀因子,A試料由原本2.57增為3.89,B試料由原本2.50增為3.04,證實共構後對壩安全更有保障。
綜合而言,易發生土石流潛勢溪流若既設許多非透過壩,由於淤積,對土石流規模降低能力誠屬有限,與平面透水柵共構,施工時不但節省成本,選址容易,同時由於各具特性而有互補功能,冀望此一創舉研究早日運用落實於現場,則既設非透過性壩附加價值能大大提昇。

Abstract
The frequency of disasters increased by debris flow after 921 earthquake happened in Taiwan. The scale of debris flow enlarged also. In order to prevent such disasters, many new works have been created. Among those works, dams are usual ways to be used. The main types of dams are closed-type and opened-type. The most problem is that both of them easy to be hit by large stones carried by debris flow. Besides, for blocking all silt behind its back, closed-type dam will lose solid contents after silt deposited at the upstream. For that reason, closed-type dam could only prevent the scale of debris flow from increasing, but could not decrease to . Viewing amount of 1420 rivers which have potency to occur debris flow in Taiwan . Where have been built so many closed-type dams, and they can't prevent debris flow actively. In order to activate ability of those dams for reducing scale of debris flow, we study on combining Bottom infiltration screen with it.
Flume experiment is the method for this study. We simulated where silt has deposited at upstream, the slope became 2/3 in original slope at upstream. And closed-type dams combined with Bottom infiltration screen crossed it. According to mechanism of scour by over-fall water theorem and Dimensional analysis theorem, we researched the mechanism of scour by over-fall water passing through co-construction. After flume experiment, we got the regression equations which could express the interaction between distance from scour center to dam, length of scour, depth of scour and slope in upstream, wide of rails gap in Bottom infiltration screen, length of rails in Bottom infiltration screen, average diameters of channel bed, wide of over-flow in top of dam. We proved that co-construction can reduce threaten in scour at downstream. Besides, we simulated debris flow passing through co-construction and observed the variation in ratio of concentration of sand and amount of sand. According to Transport equation and Dimensional analysis, we resolve the interaction between ratio of concentration of sand and wide of rails gap in Bottom infiltration screen, length of rails in Bottom infiltration screen. And got regression equation with those parameter and factors also. Finally, we proved that Bottom infiltration screen can promote the ability for preventing debris flow passing through co-construction. After 1134 times flume experiment, we proved that the closed-type dam could only reduce the concentration of debris flow with average less than 5.7%. By combining with Bottom infiltration screen, the closed-type dam could increase the average of concentration of debris flow to 30.3% ~ 56.8%. With combination, the average of reducing concentration of debris flow would be 570% to 890% than by Check-Dam only.
After analysis, we knew the capability of reducing concentration of debris flow could be over 25% when the value of b/d95 is less than 0.99 after debris flow passing through co-construction.
Proof from flume experiment, the depth of scour center after water passing through co-construction was less than closed-type dam only. The rates of relative reducing depth of scour center were more than 0 in general and the length of scour and distance between scour center and closed-typed dam was longer under same comparison after combining both. The rates of displacement between scour center and closed-type dam were less than 0 in general. The factor of shape of scour was 2.57 after water passing through Check-Dam in Sample A. It increased to be 3.89 after passing through co-construction. The Sample B increased from 2.50 to 3.01. Those proved that co-construction could make Check-Dam more secure and safer than before.
In a word, when closed-type dams have been built only, the capacity of reducing scale of debris flow is limited due to silt deposited at its upstream. If dams could combine Bottom infiltration screen. Not only can save budget in works for preventing debris flow, easy to choose address for constructing works, but also can be complementary to each other. We hope the result of this originality can achieve in reality. Therefore, the margin value in closed-dam can be promoted.
URI: http://hdl.handle.net/11455/34064
Appears in Collections:水土保持學系

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