堰塞湖溢頂潰壩之試驗研究

Abstract

本研究以渠槽實驗模擬堰塞湖溢流破壞之過程。實驗中壩頂受到均勻之沖刷而不致產生局部潰口，為全斷面沖刷之一維動床過程。利用數位攝影機擷取到之影像來對水位歷程與水位變化速率、壩體剖面破壞過程與水流沖刷能力等進行探討；藉由無因次因子間之關係得到迴歸式，並與現地案例進行比較。

實驗結果發現，在壩體溢頂沖刷過程中，會分別出現反射波與退水波，可由水位變化速率的歷程中之最高與次高值來判別。而水流沖刷能力與水位變化速率存在有對應關係，主要沖刷階段發生於水位變化速率之最高值與次高值之間。

利用實驗數據獲得之迴歸式歸納(在壩體下游坡角α = 35.5∘時)，當壩體縱剖面類型為平坦型或稱矮長壩(寬高比，B/H ≥ 7.20)時，其入流總水體積與壩體體積之比值將大於1800；而當壩體縱剖面類型為高聳型或稱高長壩(7.20 > B/H ≥ 1.20)時，其比值將介於240 ~ 1800之間。

This study focuses on flume experiment to demonstrate the overtopping failure of landslide dam, and the purpose of this experiment is to observe and record the failure process. In the experiment, dam crest receives uniform erosion without encountering breach, so it can be considered as full-section erosion, i.e., one-dimensional mobile-bed process. Using the images captured by digital video camera, we discuss stage hydrograph, stage changing rate, dam profile with time, erosive capacity, and so on. Besides, using the functional relationship between dimensionless variables, we can obtain regression equation then compare it with field cases in Japan.

Experimental results show that, during the overtopping failure, reflected wave and retreated wave occur respectively. We can discern them by the highest stage change rate and the second. There is a corresponding relation between erosive capacity and stage change rate. Major erosion happens between the highest stage change rate and the second.

Taking the regression equation which is obtained from experiment data, under the condition of that slope of downstream face is degree of 35.5, it can be concluded that when the dam profile is flat (B/H ≥ 7.20), the ratio value of total inflow water volume to dam volume would be larger than 1800; when the dam profile is sharp (7.20 > B/H ≥ 1.20), the ratio value would be between 240 and 1800.