Abstract
Slope stability on Bong mine is crucial for securing a balance in the gross national product of Liberia. The mine is being operated using conventional open pit methods with slope angles optimally designed to maximize ore stripping quantity. However, a working slope has displayed signs of uncertainty. The overall inclination of the slope is 56°, and the proposed maximal excavation is 315.42 m, but current depth in ore is approximately 50%. Based on the study of slope geological characteristics, the physical and mechanical parameters of rock mass and the geometrical calculation of stoping, the study is tailored on the mechanism of inspecting stress-strain behavior in response to seasonal variation of rock moisturization as a more suitable means of stope slope stability analysis in this case. This study took full account of local rainfall and other meteorological conditions. Slope stability is investigated via stereographic projections and stability assessment using the Shear Strength Reduction (SSR) method based on FLAC (Fast Lagrangian Analysis of Continua) numerical modeling technique in three dimensions to predict the stress-strain behavior of the open-pit slope and evaluate its stability state. Global stability has been analyzed under natural and saturated conditions and it is found that the slope is critically stable and needs proper attention.
Highlights
A slope may be properly designed and implemented, yet suddenly becomes unstable and collapse at an alarming rate
Slope stability is investigated via stereographic projections and stability assessment using the Shear Strength Reduction (SSR) method based on FLAC (Fast Lagrangian Analysis of Continua) numerical modeling technique in three dimensions to predict the stress-strain behavior of the open-pit slope and evaluate its stability state
The present work investigated the 315.42 m depth slope at Bong mine for stability under saturated and unsaturated conditions and the result indicated that direct and continuous rains lead to soak of wall rocks, which lowers cohesive force and affects the overall shear strength during the raining season
Summary
A slope may be properly designed and implemented, yet suddenly becomes unstable and collapse at an alarming rate. Evaluation of slope stability in the open pit mine at dif-. Bong Peak Mining project, owned and operated by China Union, is planned at 24 Mton (million metric tons) of ore per annum. The periodical rock mechanics parameters were obtained by means of Rock Quality Designation (RQD) statistics, Rock Mass Ratio (RMR) classification, Hoek-Brown analysis. The similar slope zoning, established by fuzzy comprehensive evaluation was divided into three main zones (A, B, C Zones), further carefully split into 12 inferior zones (A1, A2, A3, A4, A5, B1, B2, B3, B4, C1, C2, C3, Inferior Zones) (Lu et al, 2013), according to the periodical rock mechanics parameters and the bottom elevation of open pit and the geometrical shapes firstly (Laubscher, 1990). Slopes are generally cut as steep as possible to maximize the resource recovery, while geological characteristics of A2 Inferior Zone (partition characterized by the worst geological conditions at the time) were used as key determinant factors for slope and step parameters
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