Comparison of radio imaging method (RIM) electromagnetic wave tomography with in-mine geological mapping in the Liddell, Bulli and Wongawilli coal seams

Abstract

The radio imaging method (RIM) of coal seam mapping relies on the natural waveguide effect exhibited by coal seams to electromagnetic wave propagation. Whenever coal seams are disrupted by a natural geological discontinuity, the waveguide disruption causes a measurable change in the wave attenuation. Attenuation measurements can be analysed directly or, if sufficient data are available by tomography, to indicate the location of the anomaly and its likely severity. Such information is of vital importance in modern underground coal mining. In February, 1987 a series of trial surveys were conducted in three Australian mines by a survey team from Stolar Inc. of the USA. The results showed that the natural wave attenuation is 46 dB/100 m in the Liddell Seam, 36 dB/100 m in the Wongawilli Seam and 13 dB/100 m in the Bulli Seam. In the Bulli Seam propagation over distances in excess of 600 m is possible. The surveys were conducted over test sites where dykes and other geological features exist. Wave propagation was clearly disrupted by the dykes and it was possible to image their location by tomographic means. An application for RIM in Australian mines has been clearly indicated.