孔隙水壓模式對紅菜坪地滑區穩定性之影響

The influence of pore pressure model on stability of Hungtsaiping area

邱芝帆(Chih-fan Chiu)

指導教授 ： 董家鈞

國立中央大學/地球科學學院/應用地質研究所/碩士(2007年)

摘要

滑動面上孔隙水壓分布對崩積層與岩盤交界面滑動之地滑地活動性影響甚巨；然而，緣於崩積層材料高度異質性及其下伏岩層岩性變化與地質構造複雜，因此，增加了地滑區水文地質特性調查與分析的困難性。本研究以南投縣中寮鄉紅菜坪地滑區為研究區域，紅菜坪地滑區位於中新世砂頁岩互層之節理岩盤上，廣布級配不良且富含黏土材料之崩積層。本研究以三種不同孔隙水壓推估方法，計算紅菜坪地區崩積層與岩盤交界面之孔隙水壓分布：(1)經現地監測孔隙水壓資料校正之邊坡地下水流有限差分數值模式；(2)水壓監測之孔隙水壓比平均值；(3)假設滑動面上總水頭為線性分布。上述三種方法所得滑動面上之孔隙水壓值，即進一步可提供作為邊坡穩定分析輸入條件，並利用邊坡穩定極限平衡法分析，計算不同孔隙水壓分布模式所得到邊坡之安全係數。結果發現不同孔隙水壓推估模式，所得之孔隙水壓分布對安全係數計算結果有一定程度的影響，其中利用數值模式以及總水頭線性分布假設計算得孔隙水壓作為邊坡穩定分析條件者，安全係數值較高，分別為FS=1.75以及FS=1.71；利用孔隙水壓比獲得孔隙水壓並進行邊坡穩定分析所獲得之安全係數則較低(FS=1.54)。另外，本研究根據地下水流動數值模式計算得滑動面之孔隙水壓值以及折減之地震力係數，進行集集地震強度參數逆分析，利用邊坡穩定極限平衡法逆推所得之抗剪摩擦角(34o)較前人利用Newmark位移法(未考慮孔隙水壓)所得到的值(30.7o)為高。然而，此逆推值較一般認為崩積層與滑動面之抗剪摩擦角高許多，紅菜坪地區於滑動時造成之超額孔隙水壓的影響，值得進一步深入探討。最後，本研究分析紅菜坪地區崩積層內發生局部滑動的情形，分析結果顯示，紅菜坪地滑區滑動塊體A常時之局部穩定性安全係數為1.27，因滑動面孔隙水壓變化受降雨影響不大，故控制滑動塊體A局部穩定性之主要因素為邊坡坡趾河岸侵蝕與地震力。

關鍵字

崩積層.水文地質 ； 紅菜坪地滑區 ； 孔隙水壓 ； 邊坡穩定

並列摘要

The distribution of pore pressure on sliding surface intensely influenced the activity of a landslide sliding along the interface of colluvial and bedrock. Since the colluvial is heterogeneous and the geologic structure of the underlying bed rock is complex, it is difficult to investigate and analyze the hydrogeological characteristics of a landslides sliding along the interface of colluvial and bedrock. This research focus on the Hungtsaiping landslide which the poorly graded and clay rich colluvial deposit on the Miocene sedimentary rock were moved during and after the Chi-Chi earthquake. Three different methods were used to estimate the pore pressure distributed on the interface of colluvial and bedrock: (1) calibrated finite difference numerical model, (2) averaged pore pressure ratio, and (3) assuming linear distribution of the total head on the sliding surface. Limit equilibrium method was used to calculate the safety factor of the landslide along the interface of colluvial and bedrock. The pore pressure distributed along the sliding surface was derived from the three methods mentioned above. The safety factors are 1.75 and 1.71 if the pore pressure along the sliding surface was derived from the numerical method and assuming linear distribution of the total head on the sliding surface, respectively. The safety factor is 1.54 if the pore pressure along the sliding surface was derived from an averaged pore pressure ratio. The back calculated friction angle of sliding surface with the pore pressure derived from the numerical model is 34 o. The friction angle is higher than the one (30.7 o) calibrated from Newmark method (not to consider pore pressure). Finally, the stability of local failure occur in the colluvial was evaluated. The safety factor under normal condition is 1.27. Since the pore pressure variation is small during the heavy rainfall, the local stability will mainly govern by the erosion of the toe of the landslide, as well as the earthquake.

並列關鍵字

slope stability ； pore pressure ； Hungtsaiping landslide ； colluvial ； hydrogeological

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