Open Pit Slope Design of Ajabanoko Iron Ore Deposit, Kogi State, Nigeria

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Journal of Mining World Express, Volume 3 2014 www.mwe‐journal.org doi: 10.14355/mwe.2014.0302.01

Open Pit Slope Design of Ajabanoko Iron Ore Deposit, Kogi State, Nigeria Adebimpe, R.A1*, Akande, J.M2 and Arum, C3 Department of Mineral Resources Engineering. The Federal Polytechnic, Ado‐Ekiti, Nigeria Department of Mining Engineering. The Federal University of Technology, Akure, Nigeria Department of Civil Engineering. The Federal University of Technology, Akure, Nigeria rasheed4u1@yahoo.com; 2akandejn@yahoo.com; 3arumcnwchrist@yahoo.co.uk

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Received 8 March 2013; Revised 2 January 2014; Accepted 9 January 2014; Published 16 April 2014 © 2014 Science and Engineering Publishing Company

Abstract An appropriate open pit slope design is the one that considers both the safety and cost aspects to minimize waste excavation. Open pit slope design of Ajabanoko iron ore deposit, Nigeria was carried out using DIPS and SLOPE/W mine softwares. Compass clinometer and Geographic Positioning System (GPS) were used to determine the dip, dip direction and location respectively of joints on the iron ore deposit and this serves as an input data in the slope design. Fifty‐two dip/dip direction values were plotted using DIPS mine software. The factor of safety of the designed slope was determined using limit equilibrium method included in the slope SLOPE/W program. In order to calculate the factor of safety for the designed slopes, inputs parameters, namely unit weight of the rock mass, internal friction angle and cohesion were used in the SLOPE/W program. The obtained result indicates that slope angles with orientation of 44/071, 50/270, 61/359, 46/178 were considered safe for the eastern, western, northern and southern section of the deposit respectively. The slope design carried out shows a factor of safety that varies from a lower limit of 2.89 to an upper limit of 3.84, and this indicates safe slopes in all sections of the deposit. Keywords Open Pit; Slope Design; DIPS; SLOPE/W; Factor of Safety; Slope Angle.

Introduction Over the years slope design has become the domain of specialist geotechnical practitioners (Tebrugge et al., 2008). Slope design is an integral part of open pit planning and requires an adequate knowledge of rock mass characteristics and the type of discontinuities that are dominant on the deposit. Over the years the slope design process in large open pit mine, has been hampered by critical gaps in our knowledge and

understanding of the relationships between the strength and deformability of rock masses and the likely mechanism of failure (Read and Ogden, 2006). While this has benefited the technology of the slope design processes, it has also alienated the responsibility of the risk versus reward relationship from the mine design engineer (Tebrugge et al., 2008). Increasingly more ore characteristic data are required for the design of safe and cost effective slope in the mines. This is because these data are used as input in most of the commercially available slope design software. Variability in rock mass conditions can be as a result of major geological structures, large fault zones, and areas of closely spaced jointing, geological structures carrying water, weak rock, intense alteration and excessive rock bridges (Dempers et al., 2011). Basically limit equilibrium method makes use of the Mohr‐Coulomb equation to determine the critical slip surface. The equation is defined by the friction angle and the cohesion. However, the idea of discretizing a potential sliding mass into vertical slices was introduced early in the 20th century (Krahn, 2003). There are numbers of approaches to assess the behaviour of rock slope using different modelling methods like limit equilibrium, analytical and kinematic tools, physical and numerical models as well as intelligent models (Verma et al., 2011). The numerical methods allow the analysis of slope stability problems involving complexities related to geometry, material anisotropy and non linear behaviour (Li et al,. 2009; Kainthola et al., 2011). Numerical methods such as the Finite Element Method (FEM) have now been successfully applied to slope stability analysis over the years (Kainthola et al., 2012). Because of certain

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