51st U.S. Rock Mechanics/Geomechanics Symposium,
San Francisco, California, USA
2017. American Rock Mechanics Association
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ABSTRACT: Pit slope failure can have devastating effects on safety of personnel and equipment, and affect profitability of mining operations. Discontinuities, groundwater, rockmass strength and pit geometry can cause slope failure. Also, mining activities (such as drilling and blasting) can alter integrity of slopes and cause failure. Thus, periodic geotechnical characterization of rockmass detailing discontinuities is important for design of stable pit slopes during mining. This paper presents results of geotechnical rockmass characterization conducted at Akontansi Central Pit of Goldfields Ghana Limited, Tarkwa. Discontinuity mapping was conducted using scanline and window mapping. Rock Mass Rating (RMR) and Mining Rock Mass Rating (MRMR) systems were used to classify the rockmass. Results indicate average RMR and MRMR of 45.18% and 38.73% respectively. It was also found that overall slope angle of ~50° and bench slope of ~60° were required to maintain stable pit slopes. Kinematic analysis with DIPS 5.1 software found the hanging wall to be threatened mostly by wedge failure, with less potential for planar and toppling failures.
Pit slope failure can impact safety of personnel and equipment, ultimately affecting profitability of mining operations. While mining activities such as drilling, blasting and material excavation can alter the integrity of slopes and cause them to fail, conditions including pit stress distribution, presence of geologic structures and groundwater, rockmass strength and pit geometry can be major contributing factors to slope failures in mining operations. Stability of rock slopes is often significantly influenced by geologic structures (bedding planes, joints and faults) of the rock in which the slope is located.
Rock slope stability analysis is routinely performed for assessing safe and functional design of excavated slopes (such as open pit mines, road cuts, etc.) and/or equilibrium conditions of natural slopes. The analysis is usually conducted to determine rock slope stability conditions, investigate potential failure mechanisms, determine slope sensitivity to different triggering mechanisms and design optimal slopes with regards to safety, reliability and economics (Eberhardt, 2003). Paul and Freiberg, 2006 state that geological investigation of rock slope is an important exercise for stability of slopes and safety of personnel. This study thus aimed to assess the stability of open pit slope at Goldfields Ghana Limited located at Tarkwa in the Western Region of Ghana.
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