運用數值計算進行楔形岩體破壞之敏感度分析;Sensitivity study of wedge failure by using numerical calculation

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题名:	運用數值計算進行楔形岩體破壞之敏感度分析;Sensitivity study of wedge failure by using numerical calculation
作者:	王重智;Wang, Chong0Zhih
贡献者:	應用地質研究所
关键词:	Flac2D/3D;楔形破壞;剛塊法;最大剪力強度法;Flac2D/3D;wedge failure;rigid wedge method;maximum shear strength method
日期:	2019-08-19
上传时间:	2019-09-03 17:01:01 (UTC+8)
出版者:	國立中央大學
摘要:	一般常見的岩坡類型可分為四種：(1)平面型，(2)楔型，(3)圓弧型及(4)傾覆型。台灣位處於造山帶，斷層、節理，等構造發達，這些構造在岩體之中相互交錯易形成楔形，因此楔形破壞在台灣須格外注意。針對楔形岩體的穩定性分析，一般採用剛塊法，其假設楔形體為剛體，不考慮岩體本身變形性，忽略不連續面上垂直於兩不連續面交線之剪力，但以真實情形來看，面對大型的楔形體時，由於岩體的裂隙多，變形性大，若使用剛塊法做分析顯然會有偏差。因此李錫堤(1989)提出最大剪力強度法，假設不連續面上垂直兩不連續面交線之剪力等於岩體不連續面之剪力強度提供的最大剪力來做分析。由於真實岩體的性質多介於剛體與變形體之間，前者常會過估不連續面上之正向力以獲得較高的安全係數，而後者則有低估兩個不連續面上之正向力以致獲得較低安全係數的情形。實際上此兩方法正好提供了楔形岩體安全係數的上下邊界。本研究為瞭解真實岩體不連續面上真實剪力大小以求得正向力來求取安全係數，擬使用數值模擬軟體Flac2D(7.0)/Flac3D(5.0)分析在不連續面上凝聚力為零時楔形體在不同的不連續面交線傾沒角、不同的面角大小及不連續面上不同的摩擦角的情況下其真實剪力為何，以求得岩體滑動前之安全係數，並找出合適的評估方式。研究結果顯示，不連續面摩擦角大於不連續面交線傾沒角時，Flac2D 與Flac3D 計算之安全係數皆在前人定義上下邊界內，且其接近最大剪力強度法之結果。Flac2D 與Flac3D 計算結果相似，故可以Flac2D 做分析較為快速。Flac3D 計算之安全係數時若不連續面交線傾沒角大於不連續面摩擦角時須使用強度折減法計算。 ;Slope failure can be divided into four categories: (1) planer failure (2) wedge failure (3) circular failure (4) topple failure. Taiwan locates on Orogenic belts. There are a lot of geological structures, such as joint and faults. These structures cross each other and form rock wedge easily. In analysis of wedge stability, engineers use rigid block method commonly. The method assumed a wedge is a rigid body, and don’t consider deformability of the wedge. Therefore, shear force perpendicular to intersection line of the two discontinuities on the discontinuity plane can be neglected. However, when we are involving a large rock wedge, fractures and deformability can not be over looked. Lee (1989) proposes maximum shear strength method for a large rock wedge analysis. He assumed the shear force perpendicular to intersection line of the two discontinuities on the discontinuity is equal to the maximum shear force offering from shear strength of the discontinuity. In reality, the property of a rock wedge is between rigid body and deformable body. The former method would overestimate normal force which makes higher factor of safety, the latter would underestimate normal force which makes lower factor of safety. Thus the two methods, rigid wedge method and maximum shear strength method, provide the upper and lower boundary of factor of safety. In this study, calculate the shear force of wedge to get factor of safety before wedge sliding. We use both Flac2D(7.0) and Flac3D(5.0) to compare which method is more suitable for calculating factor of safety in different cases by using different plunges of intersection line of two discontinuities, different dihedral angles and different friction angles of discontinuity. The result of this study shows that if friction angle of discontinuity is larger than plunge of intersection line of two discontinuities, factor of safety calculated by Flac2D/Flac3D are between boundaries calculated by previous study and it is close to the result of maximum shear strength method. In addition, because the result of Flac2D and Flac3D is similar, Flac2D can be used for faster analysis When Flac3D is used, if friction angle of discontinuity is smaller than plunge of intersection line of two discontinuities, we should use shear strength reduction method to calculate factor of safety of the wedge.
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