166線80K地滑區滑動機制之研究

Abstract

166線80k地滑區位於嘉義縣梅山鄉瑞里村，近年來遭逢暴雨侵襲即有地層滑動災害發生，尤其以2009年8月之莫拉克颱風造成之滑動破壞最為嚴重，初步估計滑動體頭部地表陷落約達1~2公尺以上。 研究區面積約40公頃，範圍東西向約450m，南北向約1,000m，地形北高南低，標高約由EL.1,115m向下遞減至EL.830m，高差約285公尺，主要保全對象為166線78K～82K沿線商、住家。本研究區共有8處地質鑽孔，深度40至52公尺不等，作為地下水位及傾度管觀測，另埋設15處坡面固定樁。 本研究區地層屬上新世卓蘭層，主要岩性由細粒至粉砂質層狀砂岩構成，與頁岩常呈薄互層組成。地層位態約為東北－西南走向，與區域地質構造走向相近，在地形上構成順向坡。海土崙溪縱向貫穿研究區域，將研究區域分為左右二岸之地形區塊，因此在地形及位態考量上，海土崙溪有沖蝕坡腳造成趾部側向支撐發生解壓破壞之可能。 經地質調查、地下水文監測等相關調查工作後，發現本地滑區為一老崩塌區，前次地質災害導致大規模坡體順向滑動，並於研究邊坡留有厚層崩積土層，因近年極端降雨導致邊坡穩定狀態超過臨界條件，是為前次崩積土體含水過重而沿平整的砂岩層面往下方移動所致。本研究區屬於高風險區，建議持續針對研究區域邊坡進行監測工作以供後續警戒與工程設計參考外，並配合防災疏散避難演練，於颱風豪雨時提早疏散至避難處所，確保民眾生命財產之安全。

This study investigated landslide at the site of Ruei-Li village, Meishan Township, Chiayi County. In recent years, this area faces with landslide disasters during heavy rainfalls. Particularly in August 2009, a landslide caused by Typhoon Morakot was the most serious than ever. The initial estimation of the head surface sliding body was about 1- to 2-meter drops. The range of the sliding area is about 1000m from south to north and 450m from east to west, with 40ha area. Terrain feature is that north-side higher than south-side. It is decreasing from EL.1,115m to EL.830m of elevation ,therefore the height difference is about 285m.Mainly conservations are stores and households along the County Highway No.166 on 78K~82K.There are 8 boreholes of 40m~52m depth as observation for groundwater level and inclinometers ,and installed 15 drilled shafts in slope. The research area belongs to Pliocene Cholan Formation formed of fine-grain and sandstone-shale. he formation attitude trends in the northeast-southwest direction closed to the geological structure. Therefore, it is formed to dip-slope. The research area divided into two parts by Haituron-River, therefore considering terrain and formation attitude, There is a good possibility of scouring at toes of slope lead to slope failure in lack of lateral bracing

From preliminary geological investigations, groundwater monitoring and other relative examinations, we found that study area is an old landslide area. Previous geological disasters have led to large-scale landslides along the body, and left in the thick layer of colluvial soils. This area is high potential in risk analysis. It recommends that for places with existing observation holes, maintain the efforts so as to achieve the desired functionality of pre-warning. In educational promotion, when typhoon strikes with dramatic rainfall, it can evacuate the public to refuge to ensure the safeties for resident lives and properties.