Rock stability analysis – A case study

The problems of the stability of the mineral-bearing structure ST2 at 560 m of depth in the east zone of Bou-azzer mine disturbs the advance of the exploitation. The geological and structural study based on field observations and the analysis of core drilling shows the presence of altered and fractured diorite surmounted by cobalt mineralization. Based on the empirical methods of Barton (Q-system) and Bieniawski (RMR) the bed rock is classified as poor quality. The analytical study made it possible to dimension supporting by bow-pieces and bolting. The existence of several types of discontinuities (fault, diaclases and joints) has made the realization of numerical simulation by the finite elements method very difficult. These discontinuities create a network of natural fractures which cut out the blocks in various forms likely to be detached or slip into the excavation, thus encouraging the infiltration of water creating pressure on the massif. The classical studies show their limits in practice for installation of supporting because they must take into account the characteristics of discontinuities. Hence a structural analysis of the massif is essential. The cracking survey of ST2 at 560 m of depth in the east zone of Bou-azzer mine at 560m of depth, and their processing by the DIPS software, showed the existence of three main families of discontinuity NW-SE with a dip of 75SW, NS subverticale and NE-SW with a dip of 57NW, and two families of minor joints NW-SE and NE-SW with successive dips of 40SW and 75SE. The analysis of fracturing surveys allowed us to evaluate the risks of falling blocks and the families of discontinuity responsible for them, and to limit the zones presenting a risk of slip and the families responsible for them. The importance of this study is of knowing how and where to put supporting to be opposed to the risk of fall and tilting of the blocks, caused by the network of discontinuities of the massif.