Study on the Stability of Tai-Shan Landslide in Tseng-Wen Reservoir Watershed

ABSTRACT The selected research site called Tai-Sun Landslide, connected arroundingthe Tseng-Wen reservoir slope,was the standard shape of bottle.There were about 4 ha. area for experimentation so that the soil and rock would exceed 150000m^3 slided into the reservoir.The objective of this study is toinvestigate the effects of reservoirwater levels and built road onthe stability of this slope. The study results show that the occurrence of landslide in this area areclosely effected by heavy rainfall and gully erosion.The depth of slidesurface is ariund 3-10 meters of colluvial layer to weathered layer bellow theground surface.The safety factor of this slope are around 0.843-1.203 when therainy climate is still. Generally,the slide surface of the landslide with the boundaryshape ofbottle is almost shallow than else.The major retaining works of this kind oflandslide are built surface drainage work onthe slope land and fill counterweight work in the gully.摘 要 曾文水庫泰山地滑地為一 標準之「酒瓶型」地滑地形其滑動之面積約有四公頃左右。由於瀕臨水庫 保護帶地區，如引起大滑動則將近十五萬立方公尺之滑動之土石會直接進 入水庫內，並漸次影響到鄰近坡面之安定，進而形成連帶之崩塌，故有持 續地予以監測與實施防治工程之必要。 由於本地滑區內之表土層與風 化岩層厚達三∼十公尺左右，質地疏鬆、破碎易為雨水入滲，故地表沖刷 、向源侵蝕及側蝕等現象發達。區內共計施設鑽孔十四處，深度均為14.3 公尺深，總計施鑽之深度為200 公尺。藉由各種監測儀器之埋設與研判為 屬於淺層之滑動，滑動深度應在高度風化與新鮮岩盤之間。於豪雨狀態下 之安全係數值為0.843∼1.203，其滑動之原因主要係在降雨時由於受到雨 水之漫流或滲入之地下水的影響，促使其坑溝之向源、向兩側與向下切割 侵蝕作用而使邊坡末端之趾部一再地受到淘刷與沖蝕而導致失去支撐與平 衡，所引起之地層滑動。 一般而言，酒瓶形之地滑，其主要特性為滑 動面甚淺，在斜面中間具有軟弱層，並形成眾多之掌狀坑溝。在防治工程 上應以地表水排除工程以及基腳壓土法工程並用，將可收穩定其邊坡之功 效