3D geotechnical models for coal and clastic rocks based on the GSR

This paper provides the key outcomes and an example of Geophysical Strata Rating GSR analysis and modelling as undertaken in recently completed ACARP Project C17009. Various examples from the project demonstrate the use of GSR for overburden characterisation and hazard planning, tailgate stability and longwall face behaviour. Borehole spacings of 200 m or thereabouts, which are typical of Bowen Basin underground operations, allow geologically meaningful 2D and 3D modelling of GSR and other parameters derived from the geophysical logs. Plots of clay content and porosity can be used, depending on their relevance to the given strata behaviour, and/or as alternative means of investigating geological features in the overburden sequence. An approach for determining the GSR in coal and carbonaceous has been successfully developed material. In coal, the GSRi is inversely related to brightness as indicated by the ash content evident in density, natural gamma and sonic logs. GSR values are shown to relate to other existing classification schemes, but arguably with more sensitivity to the weaker materials than present in the manual logging methods.