A failure of the Pit IA highwall in July 1989 led Newcrest Mining Ltd's
Telfer Gold Mine to commence underground operations approximately 12
months ahead of schedule. The failure presented four major challenges to
management: 1. how to maximise the recovery of the Middle Vale Reef (MVR) in
the open pit: 2. how to minimise the risk to personnel involved in the extraction of
the remaining open pit ore; 3. how to avoid disruption to ore supply: and 4. how to maintain a permanent and safe means of accessing the
underground operations from the base of the pit. The risks associated with meeting these challenges were minimised
through the installation of a complex network of real time slope
monitoring equipment. These monitors were connected to an alarm
system which was combined with detailed operational procedures to be
carried out in the event of a highwall alarm being triggered. The accuracy with which the risk of failure has been managed was
demonstrated recently when the onset of a second failure was initially
identified some 13 months prior to its ultimate collapse in October 1992.
The location, timing and size of the failure was able to be predicted
allowing appropriate precautionary measures to be taken to ensure safety
of access to the underground portal and pumping equipment in the base of
the pit. This paper reviews the sequence of events leading to both the July
1989 and October 1992 failures of the Pit 1A highwall and the monitoring
equipment and procedures used to identify, quantify and manage the risk
to personnel operating in the base of the pit.