Assessment of the Stability of the North Western Flank of the Ruashi II Open Pit Mine Southeast of the City of Lubumbashi - Numerical Approach

The main objective of this study was to analyze the geometric parameters of the northwestern flank of the Ruashi II mine in relation to the geomechanical characteristics of the host rock if they are respected. This flank experienced a slope failure of the stopes slopes that washed away 177m3 of earth, which hampered the mining operations for several months. To do this, modeling based on the measurements of discontinuities, discriminated a family of stratification whose orientation is 87/311, two families of breaks oriented 77/45 and 46/117 and a westward sliding plane whose orientation parameters are 44/300. Samples taken from the three formations on the flank up to the current operating level have been used to determine the geomechanical parameters that were used to assess the margin of safety with respect to the rupture. After implementation of the 2D model obtained on the area under study by performing two cuts, the result showed that the safety factor was satisfactory. The landslide that occurred at the Ruashi II site is due to the saturation of the soil by the infiltration of runoff water through the tensile cracks in the Saprolite. This resulted in a decrease in cohesion and an increase in specific weight in the geological formations. For its protection, a surface drainage upstream of the unstable zone by digging gullies and percolation drains at the foot of the bleachers is to be considered.