Authors: Newcomen, HW; Schmidt, E; Sabo, S

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Newcomen, HW, Schmidt, E & Sabo, S 2023, 'Evolution of the pit slope design process at Western Mesquite Mines', in PM Dight (ed.), SSIM 2023: Third International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 143-160,

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Open pit mining has been ongoing at Western Mesquite Mines since the early 1980s. This low-grade gold deposit is located in a structurally complex geologic regime of metamorphic rocks beneath up to 120 m of tertiary sediments ranging from silts to conglomerates. Original slope design angles were relatively steep, did not differentiate between the surficial and bedrock geologic units, and resulted in frequent slope instability events. Through a process of slope performance evaluations in historically mined pits, back-analyses of failures, rock mass quality mapping, and geotechnical drilling and laboratory testing, slope angles have been optimised for the geotechnical units encountered in the various pits at the mine. The Brownie Pit is the most recent pit to be designed and mined. The performance of the slopes in the Brownie Pit during the first phase of mining indicated that the design slope angles were appropriate, with one multi-bench instability in the rock and manageable deformations in the tertiary sediments. This case history outlines the evolution of the investigation and design process in this unique geologic environment, and illustrates how ongoing geotechnical characterisation and documentation of slope performance can deliver optimised slope designs, improved mining productivity and safer working conditions.

Keywords: pit slope designs, back-analysis, slope performance, case history

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