Geological anomalies such as faults, sandstone intrusions, sudden thinning and severe undulation of coal seam will greatly affect the production and safety of mining operations. Since most of these geological anomalies in coal mines can increase the attenuation of the electromagnetic signal, the radio imaging method (RIM) is capable of locating the zones of geologic anomalies in underground mines. By using a low frequency EM signal, the RIM technology is the most promising geophysical tool for exploring the geological anomalies ahead of the modern longwall faces which are normally wider than 1,000 ft. However, when a number of anomalies co-exist in an area (very common), it becomes difficult for the RIM technology to differentiate the contributions of each individual anomalous factor. This will affect the interpretation accuracy of RIM technology.

In order to increase the accuracy of RIM technology, physical modeling has been employed to investigate the capabilities and limitations of RIM technology. In the scale models, the coal seam, the floor and roof strata and the geological anomalies are simulated with properly chosen simulation materials. Based on the physical modeling simulation theory and laboratory test, different ratios of sand, gypsum, and cement are used to build the floor and roof strata in the scale models. A mixture of sand, coal powder, gypsum was used to simulate the coal seam. Due to the small size of the physical models, a high-frequency EM signal has to be used in the model testing to ensure the “similarity” between the actual longwall panels and the scale models. In a modified radar instrumentation setup, two 900 MHz ground penetrating radar (GPR) antennas are used as the RIM transmitter and receiver, respectively. RIM surveys were then conducted on the scale models. The testing data were used to generate attenuation rate tomograms which in turn were compared with the embedded geological anomalies.

In this study, the theory of applying EM method on scale physical modeling is presented. The designs and constructions of the scale models to represent different geological anomalies are described. The tomogram software is developed and validated. The testing procedure and results are also shown. The generated tomograms are analyzed against the known geological anomalies.