Analyses of the Seismic signals and Self-potential from an erosion test of a dam model and slope model

本研究於南投縣仁愛鄉的惠蓀林場二號橋下之溪床，建立模型壩潰決試驗場趾。並於2017年09月22日、2017年11月02日、2018年04月26日堆置一個平均高度約4 m的模型壩與3 m的模型邊坡進行三次潰壩試驗。本研究主要探討崩塌事件的震動頻率特性及判斷崩塌、洪水波到達時間點等。因此於模型壩、模型邊坡及下游河岸裝設加速度規、非極化電極來量測本試驗過程中所產生之震動訊號與自然電位。本研究以Hilbert-Huang Transform 的方法來分析震動訊號，分析壩體、邊坡及河岸受沖蝕所產生的震動訊號頻譜值的變化。並且在模型壩上、下游河岸與模型邊坡上劃定水位標尺，利用攝影機的方式觀察洪水進退歷程。結果顯示，透過水位高度的變化、震動訊號頻譜值強度可對應模型壩從溢頂到潰口開始劇烈向下侵蝕之過程，並可由頻譜值曲線輔助推測壩體材料幾個崩塌事件的時間點。而由模型邊坡的震動訊號頻譜值強度的變化也可對應水流沖蝕過程與崩塌事件的時間點並分析其震動頻率分佈。而由模型壩與模型邊坡的電極量測結果顯示，當水碰觸到非極化電極時自然電位會隨之上升，電極附近發生位移時，自然電位會下降。自然電位之變化可以對應至模型壩的蓄水到潰決破壞過程。也在模型邊坡試驗中，發現自然電位可以對應邊坡受到洪水沖蝕導致崩塌的過程。The model was built in the creek at Huisun Forest Area, Nantou County. This study a dam model of average height 4 m and a slope model of height 3 m for a dam erosion test. The process of investigation totally 3 times in September 22, 2017, November 02, 2017and April 26, 2018. Our goal is investigate the vibration frequency of collapsing and decide the time of collapsed and flood flushed. This study installed accelerometers on top of the dam and slope and downstream riparian and non-polarized electrodes to detect the seismic signals and the variation of the self-potentials of the dam and slope. The seismic signals were analyzed by the Hilbert-Huang Transform method to obtain the time-frequency spectra and the curves of the spectral magnitudes versus time. The water level scale is defined on the model this study set, and we observe the flood process by the camera. This study identified when the collapsing/sliding events occurred and the range of the vibrational frequency. The erosion processes of the dam and slope can be corresponded to the curves of the spectral magnitude too. From the self-potential results, this study found that the self-potential value increased when the water level reached the positions of the non-polarized electrodes. When an electrode displacement occurs, the natural potential drops. The variation in natural potential can correspond to the impoundment of the model dam to the collapse process. This study also found the model slope procession that the natural potential corresponded the slope collapsed by flood erosion.目錄 第一章 緒論 1 1.1研究動機與目的 1 1.2研究內容 1 1.3研究架構 2 第二章 文獻回顧 4 2.1 震動訊號 4 2.2自然電位 5 2.3希爾伯特-黃轉換法(HILBERT-HUANG TRANSFORM, HHT) 7 第三章 研究方法與材料 8 3.1希爾伯特-黃轉換法 8 3.2 自然電位法 10 3.3試驗儀器介紹 10 3.3.1加速度規(Accelerometer) 10 3.3.2非極化電極(Non-polarizable electrode) 11 3.3.3資料擷取器 11 3.4試驗儀器配置 14 第四章 結果與討論 25 4.1第一次(2017.09.22)模型壩潰決試驗結果與討論 25 4.1.1模型壩-震動訊號 25 4.1.2模型壩-自然電位 32 4.1.3模型邊坡-震動訊號 34 4.1.4模型邊坡-自然電位 40 4.1.5下游河岸-震動訊號 42 4.2第二次(2017.11.02)模型壩潰決試驗結果與討論 58 4.2.1模型壩-震動訊號 58 4.2.2下游河岸-震動訊號 66 4.3第三次(2018.04.26)模型壩潰決試驗結果與討論 82 4.3.1模型壩-震動訊號 82 4.3.2模型壩-自然電位 93 4.3.3模型邊坡-震動訊號 97 4.3.4模型邊坡-自然電位 108 4.3.5下游河岸-震動訊號 111 第五章 結論與建議 127 5.1結論 127 5.2建議 128 參考文獻 12