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標題: The Investigation on Landslide of Lichi Formation at Da-Po Hillslopes in Fu-Li , Eastern Taiwan
作者: 吳志展
關鍵字: Lichi Formation
Eastern Taiwan
出版社: 水土保持學系
摘要: 利吉層為台灣東部地質成份之主要成因之一,利吉層之特性為由巨厚的灰色泥岩夾雜多種大小不一之外來岩塊所組成,具有複雜的錯動和剪移,而且缺乏明顯的層理。利吉層內的外來岩塊直徑大部份都在數公尺以內至數公厘大小,少數巨大的岩塊,則可以大到一平方公里以上的面積。利吉層岩層脆弱地質,其強度及穩定性甚差。 地滑發生的原因不外乎受自然的地質構造、降雨、地下水、地震、河岸侵蝕以及人為的開發破壞所影響,在地滑之防治上,如應用各種調查、觀測以及試驗研究,予以探討引起滑動的各種原因與究明其滑動機制後,才可以防治工程方法抑制其發生,並將災害減至最少程度。本論文特以花蓮縣富里大坡山為試驗地,地質構造以利吉層為主,探討其造成地滑破壞之原因及如何採取有效治理方法,以提供對治理時之參考對策;為求對整個區域之地滑特性有所瞭解,綜合觀測之資料與分析結果歸納如下: 本試驗地地滑發生之原因除與降雨量有關之外,和利吉層上所覆蓋崩積土之土壤膨脹特性(膨潤石類土壤)亦有直接之關係。大坡山之地滑災害其滑動深度在3∼5公尺之間,表土崩積層內之排水良好,造成坡面崩壞主要原因係由於利吉層與崩積層層間,當降雨發生時由於滲透作用使地下水位上昇與地下水於層間流動之狀況,使得間隙水壓增高而使土壤抗剪強度減弱,由坡底部產生漸進式的破壞並往上延伸。
Lichi Formation is the major geological formation of eastern Taiwan. The Formation is mainly consisted of huge gray mudstones and mixed with externally imported rock material which possessing various grain sizes. In addition, the Lichi Formation without perceptible stratification has experienced very complicate stress histories and geological deformations such as compression and shearing. The grain size of imported rock material of Lichi Formation can range from few minimeters to few meters in diameter. Nevertheless, some huge rock mass can extend to one square kilometer in area. Meanwhile, the Lichi Formation appears weak and broken geological structure with low material strength and unstable characteristics. The occurrence of landslide may be resulted from inherent unstable geological structure, rainfall, groundwater fluctuation, earthquake, Montrnorillonites, and erosion. In order to investigate landslide failure mechanism of Lichi Formation, the DA-PO hillslope area was selected as an experimental sites. For instrumentations, boring exploration, inclinometer, extensometer, strain gauge and ground water indicator were installed to collect the required data. The instrumentation project was performed for one-year duration and the observations were employed for the analysis. According to the analysis, some findings can be presented as follows: 1. The displacement of the instrumented slope is significantly dependent on the intensity of the rainfall during the typhoon period. 2. The pattern of landslide in DA-PO district is a shallow type of collapse. The sliding failure surface is located at 3~5m below the ground surface under low ground water table and drained condition. The road construction and heavy rainfall may be the main causes for the occurrence of landslide.
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