Authors: Rougier, M; Castro, LM; Birchall, D


DOI https://doi.org/10.36487/ACG_rep/1308_28_Rougier

Cite As:
Rougier, M, Castro, LM & Birchall, D 2013, 'A case study on actual water pressure measurements at an open pit excavated in strong, tight rock and the implications for slope design', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 445-453, https://doi.org/10.36487/ACG_rep/1308_28_Rougier

Download citation as:   ris   bibtex   endnote   text   Zotero


Abstract:
Precedent experience is that deep open pit slopes in strong, tight rock masses with high groundwater pressure will not exhibit rock mass failure. The phenomenon is not disputed. It is noted that simple limit equilibrium or finite element slope stability models, often relied upon in mine design and feasibility assessment, can indicate the contrary for high groundwater pressure conditions. In part this is because case history examples on actual groundwater pressure information from this type of open pit are limited. Consequently, over-conservative groundwater conditions can on occasion been assumed for stability analysis purposes. This paper presents a case study of the results of actual measurements of pore water pressure during pit development using vibrating wire piezometers. They were taken for the purpose of addressing risk management concerns over non-conservative stability analysis results for pit deepening and expansion of the Williams open pit at Barrick Gold's Hemlo Operations. The property is situated on the north shore of Lake Superior near Marathon, Ontario, Canada, in an area of moderate hydraulic recharge. The actual drawdown cone was found to be tight to the pit shell at depth, yet broader than expected near−surface. This may have been due to structural features and the interpreted effect of blast damage or the combination of slow excavation and moderate recharge. Site-specific observations are presented in terms of their implications for future slope design at Hemlo and in terms of the groundwater aspect of slope stability modelling in tight rock in general, particularly where limited information is available.

References:
Dowling, J., Reidel, J. and Beale, G. (2011) A Review of Key Factors Affecting Mine Dewatering and Slope Depressurization, in Proceedings International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering (Slope Stability 2011), E. Eberhardt and D. Stead (eds), 18–21 September 2011, Vancouver, Canada, Canadian Rock Mechanics Association, Canada, CD-rom only.
Hoek, E. and Bray, J. (1977) Rock Slope Engineering, Revised 2nd ed., groundwater condition chart in Chapter 9 on p. 233, Institute of Mining and Metallurgy, Spon Press, London, 402 p.
Mathis, J.I. (2011) Photogrammetric Discontinuity Mapping as Applied to Structural Interpretation and Drillhole Planning at Barrick’s Williams Pit, in Proceedings International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering (Slope Stability 2011), E. Eberhardt and D. Stead (eds), 18–21 September 2011, Vancouver, Canada, Canadian Rock Mechanics Association, Canada, CD-rom only.
Mikkelsen, P.E. and Green, G.E. (2003) Piezometers in Fully-Grouted Boreholes, Field Measurements in Geomechanics, in Proceedings of the 6th International Symposium on Geomechanics, F. Myrvoll (ed), September 2003, Oslo, Norway, pp. 545–553.
Read, J. and Stacey, P. (2009) Guidelines for Open Pit Slope Design, CSIRO Publishing, Taylor & Francis Group, Spon Press, London, New York, 496 p.
Wyllie, D. and Mah, W. (2004) Rock Slope Engineering, Civil and Mining, 4th Edition, Figure 8.4 on page 182 in Chapter 8, Spon Press, Taylor Francis Group, London and New York, 431 p.




© Copyright 2022, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
Please direct any queries or error reports to repository-acg@uwa.edu.au