顆粒型土坡模型之滑動與入滲破壞

Abstract

台灣山坡地開發日益增加，探討邊坡破壞的機制也顯得更為重要，然目前對於邊坡破壞機制之研究多為定性之描述，故若能更深入了解邊坡破壞的機制，並事先評估邊坡破壞後的行為與影響範圍，即可在災害發生前有效抑制或減少災害帶來的損失。 本研究之模型試驗主要分為兩部分：乾顆粒性土坡之破壞行為與模擬水由坡頂入滲引致之邊坡破壞。觀察乾土坡之破壞行為，係使用質點影像測速儀(PIV)分析邊坡滑動之影像，並對於各項變因（上坡坡角、下坡坡角、與上坡高度）進行探討，以建立顆粒滑動過程之位移軌跡與運動速度之理論式子，藉以預測邊坡破壞後的滑動位移、速度與影響範圍等。並考慮到水為影響邊坡破壞的重要因子，故亦模擬水由坡頂入滲，觀察地表下有不同傾角之不透水層邊坡之破壞情形，及滲流時間與影響範圍之關係。 由試驗結果得到以下結論：(1)滑動破壞行為中，滑動體前端位移與時間之關係，符合牛頓運動定律之運動方程式；(2) 影響進入水平堆積區的速度折減與堆積範圍的重要因子依序為下坡坡角、上坡坡角、與上坡高度；(3)滑動砂土達到最終範圍所需之時間，與滑動砂土量無關，而與上下坡之角度差成反比的關係；(4)水由坡頂入滲引致邊坡破壞的試驗結果，發現邊坡破壞是由坡腳先產生管湧，而後導致上坡之崩塌。

Due to the increase of over-development in mountainous lands, slope stabilities become more and more important. Present studies about slope mechanisms are mainly in qualitative description. If the understanding of the mechanism can be improved, then the assessment of the behavior and the influence area that induced by slope failures can be effectively prevented on the loss of lives and properties. This experiment comprise two parts: the study of dry granular soil slope failure and the water infiltrating slope failure. To observe the granular soil behavior, the Particle Image Velocimetry (PIV) is used to analyze the sliding images. The effects of variables are analyzed to develop formulae which can be used to predict the speed, the displacement of a sliding mass, and the influence area caused by the slope failure. Considering water is an important factor of slope failure, the conducted experiment through infiltrating from the crest of the slope for different inclinations of bedding conditions is discussed with the failure situation, the infiltrating time and influence area. The conclusions obtained from the test results are:(1) Newton’s law of motion can be applied for the displacement of soil movement; (2) The important variables in order are: down-slope angle, up-slope angle, and up-slope high; (3) The time of arrival in the deposition has no connection with the quantity of sliding mass, and it has an inverse relation with the difference of the up-slope and the down-slope angles; (4) Regarding with the experiment of water infiltrating into slopes, the slope failures are initiated with piping at the toe of the slope, and then progresses upwards until the whole slope collapses.