IOSR Journal of Applied Geology and Geophysics (IOSR-JAGG) e-ISSN: 2321–0990, p-ISSN: 2321–0982.Volume 5, Issue 3 Ver. I (May. - June. 2017), PP 21-33 www.iosrjournals.org DOI: 10.9790/0990-0503012133 www.iosrjournals.org 21 | Page Review of Weathering and its Potential Effect on Mine Slope Factor of Safety Chakufola S 1 , P R K Chileshe 2 , E B Samuel 3 1,2 Department of Mining Engineering, Copperbelt University, Zambia 3 Department of Mathematics, Copperbelt University, Zambia Abstract: Introduction: Weathering is the transformation of lithological, chemical and physical character of a rock or soil in a mined slope, after excavation when it is exposed to atmospheric agents and derivatives. The changes caused degenerate the mechanical and physical strength of a rock or soil, which compromises the stability of mined and backfilled slopes during mine operations. Problem: Some slopes at a Zambian Copperbelt open pit mine site, have been observed to experience various degrees of weathering which has contributed to a number of slope failures. Objective: In this paper, the main objective was to evaluate the influence of weathering on the geotechnical properties of materials on pit slopes through the computation and evaluation of factors of safety for slope stability in weathered and un-weathered strata. Method: Desk studies were conducted with detailed review of the available company, national and global literature concerning the effects of weathering on geotechnical properties as well as past reports on the weathering effects on slope stability at the study site. Mining and geotechnical personnel were also interviewed, followed by reconnaissance slope survey in various open pits at the mine to assess and verify the degree of weathering and related slope instability. This facilitated the building of a qualitative and quantitative geotechnical database which was used to provide or estimate input parameters for computation of factors of safety for slope stability for weathered and un-weathered strata. This was followed by computation of the factors of safety for open pit slopes alternating five different rock formations using moments analysis and AutoCAD Fellenius type construction for slope failure (to toe) and base failure (below toe) as well as, for comparison as an independent benchmark, a commercial computer software “SLIDE”. Weathering in mined slopes for slope stability was simulated by downgrading measured input parameters, specifically, cohesion, friction angle and density. Results and interpretation: At the mine site, weathering in mined slopes varied from imperceptible in strong siliceous/quartzitic rock to very pronounced in some areas, and sometimes even within the same slope, especially those of mixed lithology, without a proven timescale as to pre- or post-mining. Water was identified as the main source of weathering in the mine strata. Contribution to weathering in the mined slopes by effects due to air were also perceptible, to a lesser extent, although hypothesised to be significant in backfill slopes due to aeration during loading, transportation and dumping. Slope factors of safety were depressed by weathering. Conclusion: It was clearly observed and calculated that weathering action reduces the rock mass strengths in weathered mined and backfill slopes. This destabilises the slopes by reducing the factor of safety with time. However, though no specialised techniques were used, but with extensive observations and using theoretical analyses, actual design parameters, computer programs such as SLIDE, AUTOCAD to draw failure profiles and EXCEL spreadsheet calculations, it was concluded with reasonable confidence that: weathering affected rock mass strength through weakening of geotechnical properties of materials on mined slopes with water as a main weathering agent. The critical factor in weathered materials appeared to be cohesion. Recommendations: To avoid aeration and water weathering of mined slopes, consideration should be given to coverage by geocomposite materials or impermeable soil like laterite. Cambering of the slope surface to provide water drainage away from slope edges is another option, which is already widely practiced by many Zambian open pits. Grout curtains to cut off strata water or river water from going into specific areas and strata of open pits have been successfully used in the past, for example, in Poland next to the Vistula River. Keywords: factor of safety, Fellenius, mined slopes, slope failure, slough, weathering, Zambia. I. Introduction 1.1 Problem Statement Most ground movement problems in slopes in the open pits at the mine site under study and around the Copperbelt [1; 2] are believed to be associated with the influence of weathering on mined pit slopes. The studied mine site was in the Copperbelt Province of Zambia, where numerous copper and cobalt ore open pits as well as dolomite quarries, for lime and cement production, have been mined in the past 60 years and continue to be