Rockmass Characterization for Open Pit Slope Design Using Kinematic Analysis

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.