dc.description.abstract | 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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