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)
Date Issued
2002
2002-07-31
Date
2002
2002-07-31
Author(s)
DOI
902625Z002022
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.
Subjects
debris flows
critical rainfall line
peak ground acceleration (PGA)
physiographic factor
hydrological factor
Fisher's discriminant function
seepage
critical hydraulic gradient
piping
electrical conductivity
SDGs
Publisher
臺北市：國立臺灣大學生物環境系統工程學系暨研究所
Type
report
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