Underground » Geology
This report presents the findings of a 12 month fundamental research project undertaken by the CSIRO Exploration and Mining. This effort was driven by the desire to investigate and identify new methods and applications of ground penetrating radar to benefit the underground coal mining industry. Ground penetrating radar is an electromagnetic-based sensing technique that can rapidly provide structural information of the subsurface without the need for drilling or excavation. It has been usefully applied to a range of non-coal investigations and hence the motivation for considering its application to coal mining problems. A review was conducted to assess the current state of ground penetrating radar in coal mining, which also included discussions and evaluations with radar system vendors. Several important documents and radar performance results were obtained as a result of this process. Rather than purchase a single ground penetrating radar system the decision was made to hire such equipment as required, which provided more evaluation options for the project. Several different radar and antenna configurations were considered. All testing was conducted using the radar system in the most convenient mode of operation, namely the reflection mode using a fixed-offset distance bi-static antenna.
Two main radar applications were considered: A long-range mode for “forward looking” sensing and a shorter-range mode for roadway evaluation.
Initial effort examined the use of ground penetrating radar as a long-range in-situ ahead-of-mining sensor in the forward looking configuration. This application was motivated by the significant operational and safety advantages that would result from the capacity to rapidly detect large voids, water bodies, faults and other important geological anomalies. To aid understanding of this forward looking scenario, a computer simulation was first conducted. A preliminary evaluation was conducted for this application using commercially available, non-intrinsically safe ground penetrating radar systems. It was found that penetration depths of five to eight metres were achieved under favourable propagation conditions. This penetration depth is generally consistent with claims made from credible sources for comparable radar and ground configurations. A useful forward looking sensor for most mining applications would need a range of 40-50 metres. Therefore, these results indicate that further research and development is required before ground penetrating radar (in the reflection mode) can be used for this application. Nevertheless, this result represents a very respectable capability and is immediately applicable to other tasks in the coal mining domain. It is firmly believed that greater penetration depths are possible with future research.
The next phase of evaluations explored the potential of ground penetrating radar for observing features in the roof and rib of an underground roadway. Monitoring roadways is a very important ongoing operational task for underground coal mining. Several in-house and field experiments at Xstrata’s Beltana Highwall Mine were conducted. Features were clearly identified at high-resolution at distances up to 3.5 metres into the roof and up to 2.5 metres into the rib. An advancement on the traditional radar representation was also achieved, whereby a topographic registration of ground penetrating radar was developed using a laser range finder. This novel contribution was developed to demonstrate the potential for detailed roadway characterisation using ground penetrating radar.
Ground penetrating radar shows significant potential to provide new sensing capabilities to facilitate many aspects of mining. However its use in underground coal mining has not yet been fully explored. More activity needs to be undertaken in order to successfully transition these results to benefit the coal mining industry.