2008年汶川地震誘發中國四川省的大光包山崩，其為汶川地震所誘發規模最大之巨型山崩，土方量高達約10.51億立方公尺。基於災前災之地形變化，以及野外調查建立之地質構造模式，推論此山崩為楔型破壞，兩滑動面為層面及高角度節理，其滑動方向大略沿著其弱面之交線方向 (N70°E/14°)，滑行距離約1900公尺。楔型破壞規模一般不大，因此，地震誘發楔型破壞之大光包山崩為十分罕見之案例。本研究主要目的是利用Newmark位移分析法計算大光包楔型塊體受震後之位移量變化。過去Newmark位移分析法常用於分析邊坡受震後之永久位移，一般常用於平面型破壞及圓弧型破壞之邊坡，楔型破壞之Newmark分析案例較少見。根據前人研究，楔型體穩定性分析之方法有剛塊法(Rigid Wedge Method)及最大剪力法(Maximum Shear Stress Method)，Ghosh and Haupt (1989)利用剛塊法進行楔型體之Newmark分析，該分析基於下列四點假設：(1)滑動塊體為一剛體；(2)不需考慮垂直於滑動方向之水平地震加速度；(3)垂直地震加速度可被忽略；(4)假設摩擦係數為一定值，不隨速度和位移改變。但這些假設並不適用於每個案例。因此，本研究探討Ghosh and Haupt所提出假設之適用性，得到下列結論：(1)當破壞形式越接近平面型破壞、弱面視傾角越小、摩擦係數越小時，剛塊法及最大剪力法之結果相差不大，在這三個條件下可用簡單之剛塊法進行塊體之穩定性計算；(2)使用剛塊法時，在弱面摩擦係數小、弱面交線傾角陡與弱面視傾角偏緩之情況下，垂直之地震加速度影響較大不可被忽略；(3)垂直於滑動方向之水平地震加速度之方向若朝向摩擦係數較低、視傾角較大之弱面及弱面交線傾角較大之條件下，有無考慮此方向地震加速度所得之塊體穩定性差異大。另根據前人針對大光包山崩滑動面材料旋剪試驗結果，建立速度與穩態摩擦係數間之關係式。將所得之速度位移相依摩擦律引入Newmark位移法，並透過剛塊法與最大剪力法計算，可得大光包楔型破壞在地震過程中之速度與位移量。結果顯示大光包之楔型體受地震力作用的影響後，並不會產生長距離滑移的現象，然而，有無考慮地下水之影響亦會造成結果不同。根據控制因素分析，本研究採用之地震紀錄地震頻率過高，可能是影響Newmark分析結果的主要原因。因此，山崩處之場址效無法評估，可能造成Newmark分析結果與事實不符。;The Daguangbao landslide which triggered by the 2008 Wenchuan earthquake is the largest earthquake-triggered landslides. The volume of moving mass is about 10.51×10^8 m3. The landslide is a wedge failure, based on the pre- and post- DTMs and the geological structure model established by field works. The two sliding planes of Daguangbao landslide are constituted by the dolomite and fault gouge and the wedge slid along the intersection line of two slip planes (N70°E/14°). Daguangbao landslide is a catastrophic giant landslide taking place through wedge failure, but the scale of wedge failure is small in common case. To analysis the stability of wedge failure, we conduct Rigid Wedge Method (RWM) and Maximum Shear Stress Method (MSSM). Ghosh and Haupt used RWM with Newmark displacement analysis to calculate the permanent displacement based on following assumptions：(1) The sliding block is a rigid block; (2) The horizontal seismic acceleration which perpendicular to sliding direction does not require to be considered；(3) The vertical seismic acceleration can be ignored；(4) The friction coefficient is constant. These assumptions are not suitable for all case of wedge failure. In this study, we explore different conditions of landslide occurrence with these assumptions and use Newmark displacement analysis combining with the Rigid Wedge Method (RWM) and Maximum Shear Stress Method (MSSM) to calculate the permanent displacement of Daguangbao landslide. We conclude three points as following: (1) We simplified the calculation of safety factor (F.S.) with the usage of RWM when the failure closes to plane failure and the friction coefficient and the apparent dip of weak planes are small; (2) The vertical acceleration can’t be ignored when the plunge of intersection line is large, and the friction coefficient and apparent dip of weak planes are small; (3) The horizontal acceleration (ah) which is perpendicular to intersection line can’t be ignored, when the plunge of intersection line is large, and the points toward the plane of lower friction coefficient and larger apparent dip of weak plane. The friction law of weak plane materials is established from rotary shear tests. The results show that the Daguangbao landslide only slips respectively 0.003 m and 0.06 m through the Newmark displacement analysis combing with RWM and MSSM. The influence of groundwater is not considered in this study, which cause a different result probably. Accroding to the analysis of controlling factors, the two station with high frequency of the seismic acceleration is the main reason which affect the result of Newmark displacement method. The results show that the frequency of seismic acceleration probably significantly impacts the Newmark analysis, and the site effect annnot be considered in the analysis.
