同步化量測流動崩塌面積與質流量之陡斜率砂箱實驗

Synchronized measurements of active landslide area and mass flow rate in steep sandbox experiments

周姿妤(Tzu-Yu Chou)

指導教授 ： 卡艾瑋

國立臺灣大學/工學院/土木工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101729

摘要

本論文以三種不同大小的角度與三種不同高度的壩口進行陡斜率崩塌實驗，本研究主要分析方法為利用長曝光影像獲取崩塌過程中的邊界範圍與面積，觀測崩塌的過程變化並建構數值地形模型。其研究目的為觀測實驗過程中崩塌面積範圍變化，且利用實驗得到的質流量、流動面積與同步化時間資訊，連結三者的關係，並進一步將此三項物理量與其他參數結合，推導出質流量和時間、流動崩塌面積和時間、質流量和流動崩塌面積之間因次化和無因次化的關聯。
從實驗觀測與分析可得知，崩塌次數不只有一次，隨著壩口高度或角度的增加，其崩塌次數和崩塌總時間也隨之增加，並可能會產生第三波到第四波的崩塌，且在第一波崩塌後，第二波的崩塌有很高機率從兩側開始崩落。在大角度的無因次結果中，不同壩口高度的數據沒有明顯一致的關係，其中觀察到角度越大時，崩塌區域愈敏感，愈容易有複雜的崩塌運動機制。
此外，從分析結果顯示質流量與流動面積呈正相關，在小角度的無因次化結果中三種不同的壩口高度所得到的無因次化結果最相符，中角度相符程度次之，最後是大角度的分析結果，在小角度的實驗分析中呈現較簡單的關聯，並可以清楚了解在較小的坡度條件下，流動面積、質流量與時間三者的關聯。

關鍵字

崩塌 ； 顆粒流 ； 質流量 ； 面積 ； 無因次化 ； 長曝光影像 ； 同步化

並列摘要

To investigate landslide behavior in space and time, this research sets up idealized sandbox experiments, in which dry sand avalanches are triggered by opening a downstream outlet. A steep sandbox is initially filled with loose sand, and sufficiently deep, wide and long to allow the basal and outer boundaries of the avalanches to expand freely. Conditions are varied by altering the sandbox inclination, and the width of the outlet. To record the time evolution and spatial development of the resulting avalanches, we used an electronic scale to monitor the mass outflow, and a camera to monitor the sandbox surface. Image analysis was then used to identify the active landslide boundary and area from long exposure images and to observe the change during the landslide process. The surface topography before and after each experiment is also acquired by laser scanning. The main experimental results are synchronized records of mass flow and active landslide area, making it possible to examine their joint time evolution and inter-relationship.
Contrasted results are obtained for different sandbox inclinations. For smaller sandbox inclinations, significantly milder than the avalanching angle, opening the outlet triggers a single avalanche wave in which the active landslide area first expands, then shrinks, producing a mass outflow hydrograph with a single peak, and a single hollow after the landslide ends. The corresponding signals for different opening widths, moreover, collapse closely when plotted in dimensionless form. For steeper inclinations, by contrast, up to nearly the avalanching angle, not only does the avalanching length grow significantly, but the behavior becomes markedly more complex. Avalanching first occurs over a central zone, for which the active landslide area grows then decays, then side hollows become activated, before the central hollow might once again become activated. The avalanching flow becomes intermittent, producing multiple mass outflow peaks, and the relationship between active area and mass outflow becomes strongly hysteretic. Signals for different opening widths, moreover, no longer collapse when plotted in dimensionless form. This indicates that the landslide behavior becomes sensitive to additional factors than those considered in the dimensional analysis.

並列關鍵字

landslide ； granular flow ； mass flow ； area ； dimensional analysis ； long exposure images ； synchronization

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