|Title:||行政院國家科學委員會專題研究計畫成果報告:土石流災害防治之研究（以南投縣陳有蘭溪為研究對象）─子計畫：土石流發生危險度即時分析及評估系統（III）||Authors:||范正成||Keywords:||土石流;臨界降雨線;地表最大加速度;特性曲法;滲流;臨界水力梯度;管湧;最高滲流線;debris flow;critical rainfall line;peak ground acceleration (PGA);characteristic curve method;seepage;critical hydraulic gradient;piping;line of seepage||Issue Date:||2001||Publisher:||臺北市：國立臺灣大學生物環境系統工程學系暨研究所||Abstract:||
本研究之第一部份以南投縣為主要研究區域，選定二十八個集水區為樣本，進行影響土石流發生之因子檢定。經過Mann 一Whitney - Wilcoxon 檢定之後發現下列五種因子對土石流發生之影響較大一即土地利用因子、土瓖粒枉大於四號篩百分比、有效集水區面積、主要河川長度與溪床平均坡度。此外，本研究亦引用多變量分析中之費雪區別函數求出南投地區土石流預警的建議公式。
921 集集大地震後，土石流危險溪流的勢能增加。本研究以地表最大加速度PGA ，配合隨時間遞減之影響函數，求取各集水區地震後修正臨界降雨線之通式。另外，利用多變量常態分佈及特性曲線法求取機率式臨界降雨線以作為發佈警報的參考。
本研究第二部分則為選取土石流發生仍然頻繁之南投豐丘野溪以及神木村出水溪上游萬年神木附近的土瓖為樣本，經過試驗後，得到現地的土瓖粒柱分佈曲線以及基本土瓖物理性質參數，並依照現地土瓖物理性質參數為原則並配合因次分析進行實驗室之滲流實驗。本研究採用DuPult AssumPtion 之矩形土壩模式，來探討臨界水力梯度，找出其最高滲流線（L 05 ) ，以及計算臨界管湧公式，其結果發現豐丘與神木土樣之臨界水力梯度皆為0 . 288 ，而豐丘及神木之臨界滲流角分別約為35 及37 度。
The main purpose of this study was to analyze the hydrologic and physiographic criteria of debris flow occurrence for a watershed. There were two parts in this study. In the first part, the equations for evaluating the critical rainfall line of debris flow occurrence were developed, and accordingly, the relationship between the decline of the critical rainfall line due to the Chi-Chi earthquake occurred on September 21, 1999 and the time period after the earthquake was evaluated. Then, a method for determining the probabilistic critical rainfall line of debris flow occurrence was proposed. The second part of this study was to investigate the effects of seepage on the occurrence of debris flow induced by piping.
In the first part of this study, twenty-eight watersheds were selected in the prefecture of Nan-Iou as the test sites. After examination by Mann-Whitney-Wilcoxon test, the following five factors were found to be highly related to the occurrence of debris flow. They were: land use factor, percentage of soil particles greater than sieve No.4, watershed area, length of main stream and average slope steepness. Aside from these, Fisher¡¦s discriminant function was used to derive the equations for debris flow warning.
After the 921 Chi-Chi earthquake, the potential of debris flow for each stream was considered to be higher. The critical rainfall lines were analyzed and revised by using a factor of peak ground acceleration (PGA) and a fUnction decreasing with time. Besides, multivariate normal distribution and characteristic curves were used to evaluate probabilistic critical rainfall lines. Subsequently, the probabilistic critical rainfall lines may be used for criteria of warning systems of debris flow occurrence.
In the second part of this study, the soil samples were collected from Feng-Chiu and Sheng-Muh where debris flows occurred rather frequently in Nan-Tou. After tests, the particle size distribution curves and basic soil physical properties were obtained. Then, using the obtained data and properties, the experiments of seepage were designed and carried out. In this study, Dupuit Assumption was used to analyze the rectangular earth dam model, so that the critical hydraulic gradient, line of seepage (LOS) and equations for calculating critical piping might be evaluated. It was found that the critical hydraulic gradients for the soil samples collected from Feng-Chiu and Sheng-Muh were both 0.288. It also found that the critical seepage angles for the soil samples collected from Feng-Chiu and Sheng-Muh were 35 and 37 degrees respectively.
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