Authors: Cristi, N

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Cristi, N 2022, 'A case study in borrow source characterisation', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 739-752,

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Early material characterisation is regarded as an important step in the mine closure planning process; however, the extents of what can be required in advancing the understanding of engineering properties from a scoping-level evaluation to construction is often underestimated. This case study seeks to scrutinise the engineering requirements in characterising a borrow source that was completed to progress the design of a stabilisation buttress into execution. By examining the granularity of the materials’ design requirements and the nuances of the constructability implications sufficiently early in the design process, we can provide insight into how a host of individual studies contributed to advancing the team’s understanding of the expected range in engineering parameters and improved the confidence level in developing tender documents. Desktop studies, subsurface investigations, and laboratory testing were completed early in the project design to gain a preliminary understanding of the material’s site-specific and long-term properties. Through a detailed evaluation of the remaining unknown parameters at each stage, it became necessary to augment this ‘limited’ sample size with testing at a scale more representative of the actual construction endeavour. Geophysical assessments, (more) site characterisations, and additional laboratory testing were completed to address remaining unknowns and increase confidence of the construction estimate and schedule. To test engineering assumptions and prepare for construction readiness, the team had to bridge the gap associated with translating the engineering designs into construction drawings, technical specifications, and material take-offs. To this end, large-scale pilot excavations were conducted to develop the borrow sources and examine variations in material processing and screening requirements. The large-scale testing shed new light on trade-offs that would be required in execution, and valuable insights were utilised to inform constructability reviews and improve the overall design. The project is currently preparing for execution readiness and the goal of the thorough characterisation described herein was to de-risk the design as it transitions from the engineering phase into construction. The borrow source characterisation is intended to provide an improved understanding of the material properties while reducing the inherent uncertainty in order to minimise construction disputes and interruptions while allowing for delivery within the assumed allowances and contingencies.

Keywords: material characterisation, buttress design, closure planning

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