近年來大規模的順向坡滑動災害頻傳，甚且發生於低緩傾角之滑坡，其經反算推估 現地滑坡之剪力強度參數C、φ 又常常甚低於試驗室試體之剪力試驗結果，兩者經常不 一致。其原因，除了可歸因於地下水的作用；誠如國際上對節理面規模效應研究之瞭解， 實際滑動面之尺寸與試驗室小試體間之規模差異，也應於反算岩坡穩定分析時一併考 量，亦即其所應採用的剪力強度參數應該給予折減，以符合現地狀況，俾使分析行為更 趨於真實狀況。 岩坡在沿弱面滑動摩擦過程中，其總體摩擦角φ 內其實包括幾何粗糙度JRC 效應或 膨脹角效益，其值具有規模效應問題且與滑動量多寡有關，並非是一固定值。故探討總 體摩擦角φ 之因滑動面規模而折減的問題，可透過處理JRC 折減的途徑進行研究；若在 岩坡弱面滑動破壞時，尚有凝聚力強度C 介入，其抗剪強度需同時考慮C、φ 二者之貢 獻組合，因此在反算試誤過程中，尚需考慮C、φ 二者隨實際滑動量不同而有不等的驅 動發揮行為，才能更貼切反推滑動岩坡的實際狀況。 因此，本計畫將依序分二年進行研究分析探討：(1) 第一年將彙集國內順向坡滑動 災害案之基本試驗資、與反算分析推測報告，增加考慮各滑動岩坡規模對剪力強度參數 之影響因素，重新進行程式模擬反算分析，試圖發現其中滑動「規模效應」對「反算分 析」時所產生的影響問題。(2) 第二年進一步考慮在弱面滑動中，C、φ 之不同時趨動或 互有消長行為，以順向坡滑動災害案之剪力－剪位移曲線試驗資料，以Mohr-Coulomb 模式，建構在各滑動位移過程中，剪力強度C(us)、φ (us)項之消長問題，並進行模擬反 算分析，探討選取剪力強度參數C(us)、φ (us)之最加組合，及其對岩坡穩定反算分析之 影響。 The large-scale landslide of dip slope with low angle weakness is frequently taken place in Taiwan. The weakening effect of ground water is usually caused this landslide with low-angle slide surface along the weakness. Numerous researches of rock joints in laboratory scale have shown that the joint shear resistance is scale-dependent. That is, the shear strength parameters such as the friction angle will reduce to a smaller value in a large scale sample. Therefore, the scale effect on the shear resistance of rock slide surface should be taken into consideration in the back analysis of rock slope stability. The apparent friction angle of rock weakness such as the rock joint or bedding plane is essentially composed of the basic friction angle and dilation angle. The effect of dilation angle depends upon the overburden stress and joint roughness. The degree of joint roughness such as JRC is strongly scale dependent. The actually friction angle of rock weakness in field scale is less than that in the laboratory scale for the same joint. This means the friction angle will be reduced in the determination of friction angle for the back calculation of rock slope stability. Moreover, the mobilization of friction angle component and cohesion component is different during the sliding of weak planes. Therefore, the displacement of sliding should be considered to determine the corresponding friction angle and cohesion in field for the back calculation analysis. The main topics of the research will focus on considering the scale effect of slide weakness and reducing the experimental friction angle to determine the optimum angle in field. The shear displacement-dependent properties of friction angle and cohesion will also.
