Failure mode analysis in different geotechnical domains of the Granite Pit
Samuel Nunoo1, Dwayne D. Tannant1 & Ben Pierce2
1
School of Engineering, University of British Columbia,Kelowna, BC, Canada
2
Gibraltar Mines Ltd., McLeese Lake, BC, Canada
Gibraltar Mine is an open pit copper-molybdenum mine located near McLeese Lake in central
British Columbia. Mine production began in 1972 by Boliden Ltd, but was deferred in
December 1998 due to low copper prices (Canadian Mines Handbook 2011). Taseko Mines
acquired the mine in 1999 and production commenced in 2004. Mining is currently underway
in the Granite Pit. The Granite Pit was flooded for several years before it was re-opened for
mining. Approximately 200,000 tonnes of ore and waste are mined each day from Granite Pit
by conventional truck and shovel methods.
Gibraltar Mine monitors the performance and response of pit walls to on-going mining
activities. The primary monitoring techniques involve the use of reflective prisms, total
stations, and wire-line extensometers. These are supplemented with visual observations of
deformations and records of ground movements.
The stability and potential failure modes of pit walls in the Granite Pit are controlled by the
orientations of geologic discontinuities, such as joints and faults, with respect to the orientation
of the excavated wall as well as water pressures. Given the importance of the geological
structures, geotechnical mapping using photogrammetry software was used to determine the
orientations and engineering characteristics of the continuous and persistent discontinuities
expected to control the stability and the deformational response of different sections of the pit
walls. The paper will discuss the challenges and benefits of using photogrammetry to map
discontinuities. The presence of extensive deposits of loose rock or talus along the lower
portion of the bench faces prevent mapping at these locations and, in some areas, the rock
mass was highly fragmented through a combination of existing joints and blast damage. Results
will be presented of efforts made to identify faults in constructed digital terrain models that
had previously been mapped using traditional fieldwork techniques.
The mapping was used to define structural domains within the Granite Pit. The intent was to
establish domains where the failure mechanisms and the rock mass response are similar. For
each structural domain, likely failure mode(s) and sizes of failures were identified. The paper
will document different geological conditions in each domain and preliminary research linking
these domains, their likely failure modes, and expected or normal pit wall movements, which
will help in the risk management of the pit walls in the Granite Pit.
Corresponding author: dwayne.tannant@ubc.ca
23rd World Mining Congress and Expo, Montreal 2013