Kalenchuk, KS, Hume, CD, Morin, F, Bawden, WF, Oke, J & Palleske, CK 2017, 'The unanticipated performance of a weak massive rock mass at depth and the added value of observational engineering', in J Wesseloo (ed.), Deep Mining 2017: Proceedings of the Eighth International Conference on Deep and High Stress Mining
, Australian Centre for Geomechanics, Perth, pp. 801-812, https://doi.org/10.36487/ACG_rep/1704_55_Kalenchuk
A site investigation for the Fresnillo shaft expansion program revealed that mylonitic shale, characterised as massive but weak, would be encountered near the planned shaft bottom and in the vicinity of large excavations required for the proposed crusher station and ore handling infrastructure. The rock mass is sparsely jointed, however, fails readily along graphitic planes of weakness in the mylonitic fabric. At roughly 950 m depth, excavations within this weak rock mass were expected to squeeze and excavation support was designed accordingly. The mylonitic shale was encountered within a ramp in a nearby region of the mine prior to shaft sinking and was observed to stand-up well with minimal ground support at 790 m below surface. This paper demonstrates the value of observational engineering where observed ground behaviour was backanalysed to improve the site geomechanical model, thus, providing an opportunity for design optimisation and risk mitigation for a major shaft expansion project.
Keywords: observation engineering, very weak and massive rock mass
Bawden, WF 2015, ‘The expanding impact of technology on underground geomechanical mine design and operations - advances, limitations and future needs’, in Y Potvin (ed.), Proceedings of the International Seminar on Design Methods in Underground Mining, Australian Centre for Geomechanics, Perth, pp. 3–20.
Brady, BHG & Brown, ET 2004, Rock Mechanics: For Underground Mining, Kluwer Academic Publishers, Dordrecht, The Netherlands.
Grimstad, E & Barton, N 1993, ‘Updating the Q-System for NMT’, in C Kompen, SL Opsahl & SL Berg (eds), Proceedings of the International Symposium on Sprayed Concrete - Modern Use of Wet Mix Sprayed Concrete for Underground Support, Norwegian Concrete Association, Oslo.
Hoek, E 2001, ‘Big tunnels in bad rock’, ASCE Journal of Geotechnical and Geoenvironmental Engineering, vol. 127, no. 9, pp. 726–740.
Holling, CS 1978, Adaptive Environmental Assessment and Management, John Wiley & Sons, Chichester, UK, abstract can be viewed at
Potvin, Y & Hadjigeorgiou, J 2008, ‘Ground support strategies to control large deformations in mining excavations’, in TR Stacey & D Malan (eds), Proceedings of The 6th International Symposium on Ground Support in Mining and Civil Engineering Construction, The Southern African Institute of Mining and Metallurgy, Johannesburg, pp. 545–560.