Hamman, ECF & Coulthard, MA 2007, 'Developing a Numerical Model for a Deep Open Pit', in Y Potvin (ed.), Proceedings of the 2007 International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering
, Australian Centre for Geomechanics, Perth, pp. 225-237, https://doi.org/10.36487/ACG_repo/708_12
Sunrise Dam Gold Mine consists of the Cleo open pit and extensive underground development from where
the extraction of flat and steep dipping tabular orebodies have commenced in the western wall of the pit. The
ultimate open-pit dimensions will be approximately 2100 m long, 1200 m wide and 440 m deep.
The pit is geotechnically demanding with mining exposing new challenges on each bench due to the varying
lithologies and complex structural geology. In 2003, a detailed structural mapping programme was started
to identify potential problematic mine-scale structures, and to evaluate the properties of the main joint sets
observed in the pit. A number of strength testing programmes were completed each year to establish a rock
mass property database.
The data from both these programmes formed the basis of the geotechnical model used to select the design
sections to be analysed using numerical analysis techniques. Four design sections were selected for the
western wall to evaluate the slope behaviour using the program UDEC. The UDEC models for each section
incorporated an explicit representation of the major joint sets within the rock mass, and also treated the rock
material strength via the Hoek-Brown criterion. Parametric studies were performed, considering two cases
of joint friction angle and both upper and lower estimates for rock material UCS. Each model consisted of
an equilibration of the pre-mining system, then excavation to the ultimate pit in three stages. Finally, rock
and joint strengths were progressively reduced for the final stage of mining, to provide estimates of the
factor of safety (FoS) of the west wall slope.
Coulthard, M.A. and Little, T.N. (1999) Modelling of stability of high westwall at Ok Tedi Copper-Gold Mine. pp. 39-
46, Proceedings for International Symposium on FLAC and Numerical Modelling in Geomechanics,
Minneapolis, USA. C. Detournay & R. Hart (eds.) Rotterdam: Balkema.
Coulthard, M.A. (2007) UDEC stress analysis models of Section F,G,H and I at Sunrise Dam Gold Mine, Unpublished
report, February 2007.
Hoek, E., Carranza-Torres, C. and Corkum, B. (2002) Hoek-Brown Criterion – 2002 edition. Proc. NARMS-TAC
‘Mining and Tunnelling Innovation and Opportunity’, Toronto, Canada. University of Toronto Press, pp. 267-
ITASCA. UDEC - Universal Distinct Element Code, Version 4.0, User Manual. Itasca Consulting Group, Inc.,
Minneapolis, Minnesota, U.S.A., 2004.
Lilly, P.A. (2002) Open pit mine slope engineering: a 2002 perspective. Western Australian School of Mines, Curtin
University of Technology.
Fowers, C. (2005) Geotechnical structural modelling: East wall project. Internal report, June 2005 (unpublished).
Fowers, C (2006) Geotechnical structural modelling: West wall project. Internal report, March 2006 (unpublished).
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