The Ernest Henry crusher chamber is a large excavation located at a depth of approximately 1 km. During the pre-feasibility study, a single exploration drill hole was extended below the orebody which identified no adverse ground conditions and the crusher location was set. Additional diamond drilling into the planned crusher chamber location was conducted in 2010 and followed by a geotechnical assessment of the life of mine chamber stability. This analysis found that the planned chamber was located almost entirely within a large fault zone, and that the chamber was likely to be unstable. The chamber was relocated as far as the constraints allowed, which ensured that there was no known fault exposure in the chamber backs although the fault zone was still exposed in the walls. The alternate chamber location was found to be more stable, but it was understood that the poor ground conditions would require heavy ground support to ensure life of mine stability. A detailed geotechnical assessment of the revised chamber location was undertaken to assess stability and support requirements, comprising of core logging, structural mapping, rock mass characterisation, empirical and kinematic stability assessments, simple numerical models and benchmarking against crusher chambers at other mines. The excavation sequence was set to minimise damage from over-mining, promote stability via the ground support installation sequence and minimise impacts on the mining schedule. Three-dimensional discontinuum non-linear numerical modelling was used to confirm the sufficiency of the proposed excavation design, sequence and ground support system over the entire life of the mine to identify potential problems and additional support requirements before the chamber was mined. Chamber construction was managed like a civil engineering project with a stringent quality control programme for both mining and ground support. An instrumentation system and ongoing monitoring programme were designed to monitor rock mass behaviour and ground support response and compare actual behaviour to the model forecasts.