Ground support in kimberlite: design and implementation challenges

Authors: Dunn, MJ; Kebatsetse, LQ Download Paper

DOI https://doi.org/10.36487/ACG_repo/2625_10

Cite As:
Dunn, MJ & Kebatsetse, LQ 2026, 'Ground support in kimberlite: design and implementation challenges', in D Cumming-Potvin & J Wesseloo (eds), Ground Support 2026: Proceedings of the 11th International Conference on Ground Support in Mining, Australian Centre for Geomechanics, Perth, pp. 1-14, https://doi.org/10.36487/ACG_repo/2625_10



Abstract:
The Jwaneng mine is a large open pit diamond mine extracting 3 kimberlite pipes. Studies are underway to transition to an underground operation by the time open pit mining ceases. Underground mining will be done using a combination of blasthole open stoping and sublevel retreat, sublevel caving and block caving mining methods. All these mining methods require significant tunnel development within the kimberlite pipes. Kimberlites are highly variable and can range from competent to very weak rocks depending on the facies. The kimberlite rocks in this study have intact strengths in the 20 to 60 MPa range; there are also kimberlite breccias which have a kimberlite matrix and country rock clasts in varying proportions and have highly variable intact strength. Kimberlites and kimberlite breccias rock masses are extremely difficult to classify using widely used classification systems such as the Bieniawski (1989) rock mass rating (RMR89) system, Q-system (Barton et al. 1974) and geological strength index (GSI) (Hoek 1994). This is typically due to the absence of open joints resulting in high rock mass ratings, whilst for the breccias, the high variability between matrix and clasts is problematic. The kimberlites have swelling clays (smectite) present in varying proportions depending on the facies. An increase in the smectite proportion increases the weatherability and swelling potential (squeezing ground) in the kimberlites. Underground mining will cause stress changes on the kimberlite tunnels resulting in ongoing deformation. These issues present both design (characterisation and classification) and implementation challenges such as ongoing deterioration and the need for thin skin liners (Bartlett & Nesbitt 2000). Ground support practices at other kimberlite underground mines in South Africa, Canada and Australia have been reviewed as part of the design process. A combination of mine experience (precedent), empirical methods, and numerical modelling were used to assess ground support requirements. An attempt to account for swelling (squeezing) ground was made by adjusting the stress reduction factor (SRF) in the Q-system. Numerical modelling was used to assess likely deformation of the kimberlite tunnels and the required ground support load.

Keywords: Kimberlite, ground support design, characterisation, swelling clays, squeezing ground

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