Open pit slope design, Olympic Dam, Adelaide, South Australia

Situated 560 km north-west of Adelaide, Olympic Dam is the world’s fourth largest copper deposit, the largest uranium deposit and the fifth largest gold deposit. The deposit also contains significant quantities of silver.  The underground mine has a mine life expectancy of 100 plus years with an annual production of 60 Mt of ore.

PSM was engaged to develop an aggressive slope design for a 4 km long, 3.5km wide and 1 km deep open pit. With a small team of expert mining consultants, PSM was also responsible for seeking open-cut expansion approval.

There was complicated rock stability due to the project being completed alongside an operational underground mine. The geotechnical environment at the base of the cover sequence was also challenging due to pore pressure and structural conditions. The 330 m of cover sequence forming the pre-strip required a major capital outlay before ore could be accessed.

Following rigorous assessment and modelling, PSM’s tailored approach included:

• Completion of an extensive core drilling and bore hole imaging program
• Collection of data and stress testing and rock mechanics testing
• Structural modelling and rock mass modelling using VULCAN
• Innovative use of discrete fracture networks to model structural controls on slope design.

Using a combination of techniques, PSM successfully delivered an innovative and aggressive solution for the client while minimising risk of slope failure. Close collaboration with BHP’s engineers and geologists, as well as other experts, resulted in an efficient and highly-successful independent peer review process. The Australian Government approved open pit expansion in 2011.

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