Authors: Fournier, M; Mercer, R; Yang, D; Miller, J

Paper is not available for download
Contact Us

DOI https://doi.org/10.36487/ACG_rep/1308_39_Fournier

Cite As:
Fournier, M, Mercer, R, Yang, D & Miller, J 2013, 'Characterisation and stability modelling in weak rock masses of the Robinson Mine', 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. 595-609, https://doi.org/10.36487/ACG_rep/1308_39_Fournier

Download citation as:   ris   bibtex   endnote   text   Zotero


Abstract:
The Robinson Mine is a large porphyry copper deposit located approximately 400 km north of Las Vegas in central Nevada. Large scale open pit mining operations started in 1908, but ceased in 1978. The property was re-opened in 2008 and the mine currently consists of five open pits. Since 2012, the mine has been operated by KGHM Inc. with a focus on expanding and deepening the Ruth pit. The pit walls were largely developed with 15 m high benches and an inter-ramp angle of 36°. This wall configuration was largely based on a pit geotechnical study in the early 1990s. In 2011, excessive slope deformation and wall failures were observed along the 300 m high north wall. The deformations were primarily within the Chainman Shale, which forms the lower half of the wall. Initial deformation control and risk mitigation efforts focused on surficial flattening of the deforming materials and on the installation of a slope monitoring radar system. By December, the mine was forced to discontinue mining in the area, which has had a significant impact on the mine plan. Preliminary back−analyses in early 2012, suggested that a circular-type failure was occurring within the highly altered and weak shale and that this unit appeared to be degrading over time The back-analyses also suggested considerably lower strengths for this unit than what was being utilised in the existing pit slope design. A geotechnical drilling program was undertaken to better understand the rock mass characteristics at these depths and to support updated slope recommendations. The results of the drilling program suggested high core recoveries in the shale and the rhyolite, even though many sections of the drill core could be crushed by hand. The rock mass was classified using the RMR system, with low ratings assigned to the low quality intervals via adjustments derived from GSI mapping of available surface exposures. Triaxial and direct shear laboratory testing was also taken on the soil-like materials. The results of this work suggested that the strategically employed RMR classification, coupled with a Hoek–Brown model, may not adequately capture the strength condition for a rock mass that varies spatially between regions of intact rock and soil-like materials. In general, the back-analysis models show considerable deviation from what would be considered as the expected condition, given the rock mass characterisation and laboratory testing available. The incorporation of a disturbance zone into the slope stability analyses overcame some of these limitations and resulted in a better match to observed slope performance.

References:
Bieniawski, Z.T. (1989) Engineering rock mass classifications, A Complete Manual for Engineers and Geologists in Mining, Civil, and Petroleum Engineering, Wiley & Sons New York, 272 pages.
Broadbent, C.D. (1972) Ruth pit: Summary of Engineering Data and Analyses, Kennecott Copper Corporation Internal Report, Salt Lake City, Utah, USA.
Call and Nicholas Inc. (1991) Robinson Mining Limited Partnership: Pit Slope Recommendations, Company Report.
Deere, D.U. and Deere, D.W. (1988) The Rock Quality Designation (RQD) Index in Practice, Rock Classification Systems for Engineering Purposes – ASTM STP 984, American Society of Testing and Materials, Philadelphia, pp. 91–101.
Hoek, E., Carranza-Torres, C. and Corkum, B. (2002) Hoek–Brown criterion – 2002 edition, in Proceedings 5th American Rock Mechanics Symposium and the 17th Tunneling Association of Canada Conference, R. Hammah (ed), 7–10 July 2002, Toronto, Canada, pp. 267–273.
Hoek, E. and Karzulovic, A. (2000) Rock Mass properties for surface mines, In Slope Stability in Surface Mining, W.A. Hustrulid, M.K. McCarter and D.J.A. van Zyl (eds), Littleton, USA, Society for Mining, Metallurgical and Exploration (SME), pp. 59–70.
Hoek, E., Marinos, P. and Marinos, V. (2005) The geological strength index: applications and limitations, Bulletin Engineering Geology and Environment, Vol. 64, pp. 55–65.
Schlumberger (2011) Technical Memorandum: Draft – Ruth pit pore pressure modelling results, Reno, Nevada, 10 p.
Sjöberg, J. (1996) Large scale slope stability in open pit mining: a review, technical report 1196:10T, Luleå University, Sweden, 229 p.
Westra, G. (1982) Alteration and mineralization in the Ruth porphyry copper deposit near Ely, Nevada, Economic Geology, Vol. 77, pp. 950–970.




© Copyright 2024, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
View copyright/legal information
Please direct any queries or error reports to repository-acg@uwa.edu.au