Automated geotechnical characterisation from geophysical logs: Examples from Southern Colliery, Central Queensland

Abstract

Conventionally, geotechnical information comes from cored drill holes. However, coring is expensive and most boreholes are drilled without or with very limited coring. Alternative ways of obtaining geotechnical information need to be found. One approach is by geophysical logging. Borehole geophysical logging is carried out routinely at coal mines. It measures various in-situ petrophysical parameters which are usually correlated with rock types and can be used for rock mass characterisation, litho-stratigraphic interpretation, orebody delineation and grade estimation. This paper presents examples of automated geotechnical characterisation from geophysical logs to identify the key strata responsible for caving behaviours during longwall coal mining at Southern Colliery in Central Queensland. The method is based on computer program LogTrans. Conventional logs such as density, natural gamma and UCS (derived from sonic transit time) logs and full wave sonic data are examined. The geotechnical units predicted from the geophysical logs are well matched with the original strata classification and core photographs. A 3D geotechnical model has been established based on the LogTrans geotechnical interpretation. The results could assist site geologists, planning and production engineers predict and manage mining conditions on an ongoing basis.