Underground » Mining Technology and Production
Objectives: The objective of this project was to evaluate the use of ground probing radar (GPR) to identify the interface between coal and roof/floor material in order to establish a suitable shearer cutting horizon within the seam.
The project was conducted with Dartbrook Coal as an industry collaborator. At Dartbrook there is a specific need to identify the interface between the extracted floor and an underlying tuff layer so that the floor cutting horizon can be accurately set. A successful measurement system will have a significant impact on the quality of the run of mine product.
Experimental Program: Initial proof-of concept underground tests were carried out at Dartbrook using laboratory prototype GPR equipment developed by CSIRO and the results were encouraging. The remainder of the project was concerned with refining the GPR hardware and mounting it in suitable enclosures so that its performance could be assessed on longwall equipment at the face under operating conditions in a hazardous zone.
The final experimental system consisted of a flameproof enclosure mounted on the shearer containing processing and display equipment and a second, non-metallic flameproof enclosure containing the radar antennas and electronics attached to the first by a 20m umbilical cord. This permitted floor coal measurements to be made in the area immediately around the shearer.
Main Findings: Using the laboratory prototype equipment, the tuff layer at Dartbrook could be clearly observed through floor coal ranging in thickness from zero to >200mm, so the applicability of GPR to coal thickness measurement was successfully established. However, more general applicability depends on site conditions, particularly electrical properties of the surrounding strata.
Suitable GPR hardware was developed to measure floor coal thickness on operating longwall equipment. This development is not suitable for long term usage in a production environment. The excemption required to fit ehe GPR did not permit the system to be used during production so that only a small floor area was available for profiling.
Recommendations: Further work is necessary using the existing system to show that GPR can be used to profile floor coal thickness over an extended area. This will require an extension of the system approval to allow operation during production and a further experimental program of data collection.
In the longer term attention should be given to producing an automated system. The best position for the coal thickness sensing system from a control point of view would be on the shearer behind the trailing drum, resting on the newly uncovered floor. Unfortunately this presents virtually insurmountable difficulties from an engineering and maintenance point of view. A more practical solution would be to set up an array of fixed GPR sensors across the face on the AFC structure. This would allow probing of a smoother section of floor. The information would require more processing before it could be used for on-line control of the shearer.