|Title:||行政院國家科學委員會專題研究計畫成果報告:土石流監測與預警系統之研究─子計畫：雨量與地下水電導度(EC) 監測方法之研究(I)||Authors:||范正成||Keywords:||debris flows;critical rainfall line;peak ground acceleration (PGA);physiographic factor;hydrological factor;Fisher's discriminant function;seepage;critical hydraulic gradient;piping;electrical conductivity;土石流;臨界降雨線;地表最大加速度;地文因子;水文因子;費雪區別函數;滲流;臨界水力梯度;管湧;最高滲流線;電導度||Issue Date:||2002||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:||
There were two parts in this study. In the first part, the rainfall data and the occurrence time of debris flow were collected, and the rainfall events in which debris flow occurred and did not occur were digitized, and finally, the basic statistical parameters of the two sample groups were obtained. Using the overlapped portion of the two groups, the probabilistic critical rainfall lines for predicting the occurrence of debris flow were proposed. The second part of this study was to investigate the relationships among seepage, electrical conductivity and occurrence of the debris flow caused by piping.
In the first part of this study, 17 first order streams in the basin of Chen-Yeou-Lan streams were selected as the samples. The physiographic and hydrological factors of the watersheds of the stream samples were investigated, collected and examined. Subsequently, five factors which were more relevant to occurrence of debris flow were found. The factors consisted of the land-use factor, percentage of soil particles greater
hen sieve No. 4, effective watershed area, length of main stream and average slope steepness. After from these, Fisher¡¦s discriminant function of multivariate statistical analysis was used to derive the equations of critical rainfall lines for predicting the occurrence of debris flow before the Chi-Chi earthquake.Some modifications were made on the critical rainfall lines for the occurrence of debris flow before the earthquake. The modifications included the land use factor, peak ground acceleration (PGA) and an influencing function which decreases with time. In order to test the modified critical rainfall lines, the rainfall data of the Toraji typhoon on July 30. 2001 were used for analysis. The results were found satisfactory.
In the second part of this study, the critical hydraulic gradient at which piping occurred, field dimension analyses were conducted and accordingly, seepage tanks were designed and fabricated. On the other hand, the variety for electrical conductivity of the water was also evaluated with the seepage experiments at the same time, and tried to estimate the relationship between the electrical conductivity and the debris flow caused by piping.
In this study, Feng-Chiu of Nan-Tou prefecture was selected as the site. The soil samples were collected from the upstream site of Feng-Chiu. After tests, the grain size distribution curves and basic soil index properties were obtained. Then, by using the obtained data and properties, the seepage experiments were designed and carried out. Therefore, the critical hydraulic gradient and the equations for calculating critical piping might be evaluated. It was found that the critical hydraulic gradients for the soil samples with the slope steepnesses of 45, 60, and 75 degrees were 0.4 16, 0.413, and 0.383 respectively. It also found that the critical seepage angle for the soil sample collected from Feng.-Chiu was 26.4 degrees.
本研究之第一部份本研究以南投地區陳有蘭溪流域17 個一級溪流為樣本，調查及收集其集水區地文與水文因子資料，並對這些因子加以檢定，選出對土石流影響較大的五個因子一土地利用因子、土瓖粒徑大於4 號篩百分比、有效集水區面積、主要河川長度及溪床平均坡度。引用多變量分析中之費雪區別函數求出地震前之預測土石流發生之臨界降雨線。本研究對地震前之臨界降雨線作了若干修正。其中包含地震後之土地利用因子、最大地表加速度（PGA ）及隨時問遞減之影響函數。據此而求出各樣本溪流在大地震後修正之臨界降雨線。為了驗證此修正之臨界降雨線，乃利用90 年7 月30 日桃芝颱風之降雨記錄加以分析與討論，其結果尚佳。
之土樣配合因次分析進行實驗室之滲流實驗，探討臨界水力梯度，以及計算臨界管湧公式，其結果發現坡度為45 、60 、75 度之臨界水力梯度分別為0.416 、0.413 及0.383 ，而臨界滲流角約為26.4 度。
|Appears in Collections:||生物環境系統工程學系|
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