Underground » Geology
Efficient and profitable coal mining is reliant on reducing mining costs which requires reducing or minimizing hazards that are likely to slow down or temporarily stop mining. Understanding the geology is a vital component in this exercise because many geological structures, if undetected, cause major disruption to mining schedules. This project was initiated to evaluate the application of radio imaging technology, RIM IV series, in the detection of geological structures in underground coal mines under Australian mining conditions. The equipment trialed was a prototype which had not been approved as intrinsically safe for Australian underground mines and thus the sites available for the trials were limited. Permission to use the equipment underground was required at the local level from specific mines, not at an industry level.
Field trials were carried out in the North Goonyella and Crinum mines in late March-early April 2003. A section of Longwall Panel 3 with suspected faults was the target in North Goonyella and a known diatreme located in a pillar between gate roads B and C was the target in Crinum. In both mines the frequency used was 70 kHz although higher frequencies were available but time constraints and equipment failure in one mine did not permit additional surveys to be completed. The data obtained during the field trials was sent firstly to Stolar Horizon, Inc. in the USA to be interpreted. Stolar Horizon Inc. is the developer and owner of the RIM IV technology and equipment used in the trials. The company had previously used the equipment in both the USA and the United Kingdom.
The data were interpreted independently by Fullagar Geophysics Pty Ltd, a group with knowledge and experience in geophysical techniques, and specifically with the earlier-used RIM II-RIM 20/20 technology in Australia.
At North Goonyella, the overall results of the survey were disappointing as the signal was too strong because there was little attenuation across the panel. Consequently the receiver equipment clipped the signal. In addition, several problems relating to the ergonomics and the lack of user-friendliness of the equipment were clearly demonstrated. In spite of conductor problems, gas problems and structural orientation, on a positive note, the RIM IV signal at 70 kHz was much stronger than previously achievable at 22 kHz with RIM 20/20. The signal travelled through the 240 m thick longwall and the RIM IV equipment provided greater resolution in a mine where previous RIM technologies had been a failure and had given very poor resolution.
At Crinum, the results of the survey were much more positive. Positive outcomes were:
- A very strong signal, shot at 70 kHz, was obtained; this was much stronger than earlier RIM 20/20 signals at the neighbouring Kestrel mine
- The tomogram produced showed the location of the diatreme and showed very good correspondence with the actual mapped location of the structure
- There were no problems in shooting through air voids or mesh that had been attached to the coal faces to prevent face failure.
On a negative note, the Crinum the survey encountered a number of equipment problems at the start of the survey and again this raised the question of the ?mine readiness' and ruggedness of the RIM IV prototype used in these trials.
The independent evaluation by Fullagar Geophysics Pty Ltd was positive. They found the RIM IV system represented a ?quantum leap? over the RIM II and RIM 20/20 systems. It was recommended that the RIM-IV, if upgraded, should be pursued further as a mine-planning tool in Australian coal mines.
Despite the limitations imposed on the project by the equipment, the RIM IV technology was adequately tested under Australian coal mining conditions. The RIM IV technology greatly surpassed the earlier RIM technologies in performance and showed that it has potential in the Australian Coal Industry with further development of the technology needed and additional testing under Australian conditions.
Following the Queensland trials, Stolar Horizon, Inc. have made changes to the equipment that should overcome some of the problems encountered during this project. However, the modifications have yet to be tested under Australian underground coal mining conditions.
In summary, the RIM IV technology was appropriately tested under Australian conditions and if the following recommendations are taken on board, RIM IV will be a benefit in detecting dykes and other structures in Australian coal mines.