摘要

　　邊坡滑動是常發生的自然災害之一，若發生在人口聚集的地區，會造成生命與財產的損失。邊坡的穩定性主要受到土壤強度、地下水滲流情況、降雨情形、外力加載等因素影響，過去已經有許多邊坡穩定之工法提高整體其穩定性，本研究以鑽孔值入混凝土柱的方式增加邊坡的阻抗力，增加邊坡淺層的穩定性，混凝土柱是由水泥（cement）、砂以及稻穀灰（rice husk ash, RHA）混合而成的砂漿製成，稻穀灰含有豐富的二氧化矽，能取代重量百分比10%的水泥，並提升混凝土柱（C-RHA column）的強度，也解決廢棄稻殼的問題。
　　本研究進行一系列的離心模型試驗，模擬C-RHA柱對增加邊坡穩定的效果，邊坡材料係以重量百分比20 %高嶺土與80 %石英砂混和，在最佳含水量12 %下使用濕搗法製作70度傾角邊坡模型，並根據試驗條件以垂直邊坡表面灌入0（無加勁）、4支（間距6.7d）、9支（間距5d）及16支（間距4d）不同數量的C-RHA柱（d為直徑），以地工離心機提供穩定增加的人造重力場，直至邊坡破壞為止。試驗過程以攝影機以及雷射位移計，記錄邊坡破壞時的過程、邊坡坡面與坡頂表面之變形量。
　　試驗結果顯示，縮小C-RHA柱之間距能延後坡頂張力裂縫發生時機，裂縫發生位置亦會遠離坡頂，亦會延後邊坡破壞時機。無加勁邊坡第一條裂縫發生於40 g，裂縫深度約0.33倍坡高，第二條裂縫在45 g時發生，並於50 g重力場發生破壞；縮小C-RHA柱之間距能提升邊坡的安全係數，間距分別是6.7d、5d與4d時，邊坡的第一條裂縫分別發生於40 g、45 g及55 g，裂縫深度分別為0.30倍、0.33倍與0.56倍坡高，第二條裂縫發生於43 g、49 g及65 g，並於48 g、55 g及65 g造成邊坡破壞。以理論破壞角 θ=(β+φ)/2 為平面之楔型體積對邊坡滑動造成之崩塌量正規化，四組模型之崩塌量分別為67 %、64.5 %、59.3 %及48.6 %，縮小C-RHA柱之間距能減少邊坡滑動的崩塌量。

關鍵字：C-RHA、離心模型試驗、邊坡穩定。

Abstract

Landslide is a typical natural disaster around the world. Factors such as slope material, intensity and duration of rainfall, earthquakes and loadings, infiltration and seepage conditions strongly influence the stability of slope because of the decrease in resistance forces or the increase of driving force. A lot of methods for increasing slope stability are already developed nowadays. This research using C-RHA columns for slope strengthening. C-RHA mortar was made of cement, sand and microsilica from fine rice husk ash (RHA). Replacement 10 % of the weight of cement by RHA would increase the strength of the column.
The effect of C-RHA columns on slope stability simulated by a series of centrifuge modeling tests which were conducted at the Experimental Center of Civil Engineering, Department of Civil Engineering, National Central University. The slope is prepared by moist tamping method at optimum water content about 12 % with a mixture material consist of 20 % of the fine content (kaolinite) and 80 % of quartz sand. The C-RHA columns were penetrated perpendicular to the slope surface. During the test, the acceleration was gradually increased until the slope failed. The process of the failure was recorded through cameras during centrifuge spinning. Cameras and laser displacement scanner record the failure process, slope deformation and ground surface change.
The decreasing spacing of C-RHA column increases the safety factor of the slope. The test results show that when the spacing between the C-RHA columns is reduced, the timing of the cracks at the top of the slope can be delayed, and the location of the cracks will be far away from the top of the slope, which will delay the timing of the slope failure. In this case delay means reaching higher g level. The first crack of the slope without column occurs at 40 g, the crack depth is about 0.33h, the second crack occurs at 45 g, and the damage occurs at the 50 g. When the spacing of the slope is 6.7d, 5d and 4d, the first crack of the slope occurs at 40 g, 45 g and 55 g, respectively, and the crack depth is 0.30h, 0.33h times and 0.56h. The second crack occurred at 43 g, 49 g, and 65 g, and fail at 48 g, 55 g, and 65 g. From the side view of the slope, the decreasing number of C-RHA column spacing will decrease the depletion mass of slope, which is the volume of displaced soil that overlies the failure surface but underlies the original ground surface. The depletions mass normalized by the volume of theoretical planar failure wedge with failure angle of θ=(β+∅)/2 are 67.0 %, 64.5 %, 59.3 % and 48.6 %, respectively.
Keywords: C-RHA, Centrifuge modeling, Slope Stability

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