Waviness or undulations of a discontinuity plane due to folding result in changes in the orientation of the discontinuities. This creates difficulties in determining the general trend of the discontinuity planes on both sides of wedges and the plunge angle of wedge-type slides. However, it is possible to draw great circles representing the discontinuity planes on both sides of the wedge with strike and dip angle changes on a stereographic net. Such a wedge may have failed in the past but may be stable presently. Frequently, back analyses of the specific failure surfaces are carried out to establish the shear strength parameters that were effective at the time of the slope failure. In this way, a better appreciation of the engineering behavior and the strength parameters of the rock mass may be obtained for the design of future slopes in similar conditions. Based on these fundamentals, this study is intended to solve this problem, which is often encountered during the back analyses. Furthermore, this new approach can also be used to determine the orientations of the wedge-forming discontinuity planes and their intersection lines using the projection techniques with high accuracy. The new technique is shown to provide better results in the back analyses conducted on wedge-type slides of sedimentary rocks such as shales.

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