| 摘要: | 楔型破壞為常見之岩坡破壞模式。Hoek and Bray 於1974年提出剛性楔塊假設(剛塊法)，透過忽略垂直兩不連續面交線方向剪力，即可順利進行擬靜態或動態穩定分析。然而像大光包這類地震誘發超大型楔塊滑動之案例，垂直兩不連續面交線方向剪力即無法忽略不計。Lee於1989提出最大剪應力法，假設垂直兩不連續面交線方向剪應力達到兩不連續面之剪力強度。上述兩分析法恰為楔型塊體安全係數之上限與下限。本研究提出一變形指數( )以反應楔形塊體變形性對垂直兩不連續面交線方向剪應力之大小，並計算剛塊法( =0)與最大剪應力法( =1)之安全係數。結果發現變形指數 對安全係數影響很明顯，因此，對於大型岩楔穩定性分析，應考慮岩楔內部構造與變形性對整體岩楔滑動穩定性之影響。
地震誘發岩楔破壞，可透過Newmark位移分析法(NDA)引入速度位移相依摩擦律計算永久位移量，兩不連續面之摩擦係數將隨地震造成岩楔沿交線向量產生之位移量與滑動速度不斷改變。本研究考慮了慣性力之影響，並考慮不連續面強度異向性(SAR：垂直交線向量與平行交線向量強度比)。結果發現雖然考慮慣性力與否對結果影響不算巨大，但是考慮慣性力推導之臨界加速度才是正確的。另外，剪力強度異向性將明顯影響永久位移之分析結果，因此，不連續面強度異向性應於NDA分析時加以考慮。
本文利用大光包山崩之層間斷層泥進行旋剪試驗，將試體浸泡於水中為了使其狀態接近現地。以正向應力為1至3 MPa與等價速度介於0.001 至 1.3 m/s完成了19組旋剪試驗，摩擦行為於 0.3 m/s以下呈現滑移強化、於0.3 m/s以上則呈現滑移弱化，尖峰與穩態摩擦係數分別為0.41~ 0.81與0.12~0.63。以大光包山崩案例利用NDA引入速度位移相依摩擦律進行分析，結果顯示，當 增加表示變形性提高時，滑移速度與位移量也會逐漸增加。探討不同剪切強度折減(SRR，範圍0到1)在兩個破壞面上不同方向的影響，結果顯示，在大光包山崩案例中當SRR從0增加至1，永久位移約增加10倍(從數公分至數十公分)。由於不同方向上的滑移速度與位移相當不同，因此不同方向上的強度折減需要被考慮於分析中。
;Wedge failure is one of the common slope failures which can be triggered by an earthquake. Hoek and Bray (1974) proposed Rigid Wedge Method (RWM), a method suited for small rock wedges, that assumes the wedge as a rigid body and ignores the shear stresses on two discontinuities to calculate driving and resisting forces under pseudo-static state and seismic load. When rockslide is massive such as Daguangbao landslide, the shear stresses must be taken into account due to rock mass deformation. Lee (1989) proposed Maximum Shear Stress Method (MSSM) that considers the shear stresses as the shear strengths of two discontinuities. The results of these two methods represent separately the lower and upper bounds of the wedge stability. This study proposes a rigid-deformable index ( ) which is substituted from 0 to 1 to calculate the factor of safety ( ) from RWM to MSSM. The results show a significant influence of rigid-deformable index on the stability of rock wedge. Therefore, the influence of internal structures which dominates the deformability of rock wedge should be carefully evaluated.
Moreover, this study using the Newmark Displacement Analysis (NDA) with velocity-displacement ( ) dependent friction law, to simulate the variation of friction coefficient on two discontinuities of rock wedge with varied sliding velocity and displacement during earthquake. This study considers the inertial forces exert on the wedges during earthquake and evaluates the influence of shear strength reduction along different directions. The results show that considering the inertial force is necessary, although the permanent displacement is only slightly different if we neglecting this effect. The shear strength anisotropy ratio ( ), which is the ratio of friction coefficients perpendicular and parallel to intersection line (I-line) of wedge, is significantly influence the permanent displacement. That is, the strength anisotropy of the discontinuities along different directions should be considered.
Rotary shear tests are performed in this study using the bedding parallel fault gouges of Daguangbao landslide which is an atypical wedge failure. The sample assemblages are immersed in the water to simulate the possible in-situ condition. A series of 19 experiments under 1 to 3 MPa and range from 0.001 to 1.3 m/s of the equivalent slip velocity ( ) were performed. The frictional behaviors exhibits an obvious slip-strengthening behavior when range from 0.001 to 0.3 m/s and illustrate the slip weakening characteristic at m/s, respectively. The peak and steady-state friction coefficients range from 0.41 to 0.81 and 0.12 to 0.63, separately.
Using NDA with dependent friction law, the analysis results of Daguangbao landslide exhibited that with increasing the rigid-deformable index ( ), the velocity and accumulated displacement rise up gradually, that is because of considering a different in deformable level in both weak planes of wedge failure. To study the influence of different shear strength reduction in both discontinuities along different direction, the strength reduction ratio ( ) is proposed in this study with its value range from 0 to 1. The analysis result shows that in the case of Daguangbao landslide, when the increased from 0 to 1, the permanent displacement increased about ten times (from several center meters to several tens of center meters). That is, the different strength reduction along different directions should be considered for the sliding displacements and velocities are quite different along different directions. |
