Authors: Dunn, MJ; Chiwaye, HT; Mogorosi, O; Gabanakgosi, K

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Dunn, MJ, Chiwaye, HT, Mogorosi, O & Gabanakgosi, K 2022, 'Developing a geotechnical model for the Jwaneng underground project', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 109-122,

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The Debswana Diamond Company (DDC) Jwaneng mine in Botswana, is a large open pit diamond mine extracting three kimberlite pipes. Open pit operations will cease in the early 2030s; studies are currently underway to transition to an underground operation at the cessation of open pit mining. It is anticipated that underground mining will be undertaken using a combination of sublevel caving (SLC) and other caving methods; mining will extend to a depth of ~1,000 m below surface. The Jwaneng open pit has been in full production since 1982 and has a mature high-quality geotechnical model that has been progressively developed and improved over many years. Debswana makes use of a geotechnical review board to guide the development of the geotechnical model. The comprehensive geotechnical model is the foundation for all the open pit and underground designs at Jwaneng. The geotechnical model comprises of several components: lithology model, major structures model, rock mass model, fabric model and hydrogeology model. For the underground studies the geotechnical model has been extended in both depth and lateral extents. In 2018 the geotechnical logging procedure was changed to incorporate parameters and rock mass indices appropriate for underground mining. The Jwaneng mine is structurally complex with many large geological structures and a variable rock mass with strengths ranging from weak kimberlites (25 MPa) to very competent dolomites (>250 MPa). The various components of the geotechnical model are regularly updated; generally, this is planned to coincide with the study stage, the intent being to meet the confidence level required for each stage. This paper considers all components of the geotechnical model but focuses on rock mass and fabric models for the underground studies. This included developing systems and workflows to allow for comparison of the pre and post 2018 geotechnical data before combining the data. Length weighted histograms and descriptive statistics for various parameters (RQD, Q’, RMR89, RMR2000, GSI, etc.) were determined for different lithologies and structural blocks to assist with defining geotechnical domains.

Keywords: geotechnical model, rock mass, characterisation, geotechnical domains

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