Geotechnical data from geophysical logs: stress, strength and joint patters in NSW and QLD coalfields

In order to appreciate the geotechnical regimes operating at any mine site a comprehensive database accessing all available borehole data is crucial. An extensive geotechnical database across the mine site area must be considered for mine planning and design. Some geotechnical parameters can be defined through the analysis of an appropriate suite of geophysical logs, including the acoustic scanner and sonic velocity logs and by incorporating a strict hybrid logging classification system. The acoustic scanner tool is becoming part of the standard geophysical logging suite used today in all stages of exploration drilling. Analysis of the acoustic scanner log can provide accurate and reliable geotechnical orientation data including joint and horizontal stress orientations. Rock strength data, including massive unit identification, can be calculated using the sonic velocity, gamma and neutron log responses. The study of patterns across three separate sites in eastern Australia shows lateral stress, strength and joint set variability brought about by variations in the geological domain. While vertical variability in rock strength downhole is often observed, the range of downhole variation in borehole breakout orientation and joint set patterns is usually minor.