To accomplish a reliable rock mass characterization and assess its influence on rock slopes stability in the Yaounde area, geological field work along with further data processing and analysis have been carried out; discontinuous deformation analysis (DDA) being introduced to be less dependent on rock strength properties. Therefore it has been established that masses are subdivided in blocks by three main joint sets (F1, F2 and F3). The key and potential key block statuses are accountable to various parameters. (1) The common key block status is that with low F1 dip angle, matching to type III class where joint friction is low; whereas its uncommon status is that with fairly high F1 dip angle, corresponding to type I class. (2) The common potential key block status corresponds to type II class, whereas its uncommon status matches to type III class, where the initially tapered blocks become secondary key blocks.


A rock mass consists of rock itself and discontinuities. Discontinuity is used as a term denoting any separation of rock blocks and having zero or low tensile strength (Palmström, 2001). It is well accepted that the intersection of discontinuities in a jointed rock mass creates in situ blocks of arbitrary three-dimensional geometry, which might intersect excavation surfaces to form discrete blocks which can be kinematically free (removable blocks) and result in slope failures (Yow, 1985; Goodman and Shi, 1995). An accurate and detailed rock mass characterization is a key for adequate slope stability knowledge. A good characterization is very dependent on the time on the site as well as the surface and underground excavations. To be less dependent on rock strength properties (discontinuity and rock mass shear strength parameters) and to derive objective results, geological field work, along with further data processing and analysis (e. g., discontinuous deformation analysis) might be a solution. The idea of discontinuous deformation analysis (DDA) presented by Dr. Shi’s innovation in 1988 led to a new method of treating the deformation of discontinuous media. Since then, DDA has been adopted to solve a wide range of complicated engineering problems and spread throughout the field of rock mechanics and engineering (Xie, 2007). With useful semi-automatic tools in predicting the performance of rock slopes (e.g., Rocsciences Inc. RSDip, Goodman and Shi's block theory, Shi’s VisKBT), this paper performs a DDA with survey data from Yaounde masses.

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