There has been much recent interest in the top coal caving method in Australia and it may become an attractive option in future. However, there is an absence of relevant data for a critical technical evaluation of the LTCC method. The combined influences of ground conditions and equipment factors on mining performance are key considerations.

AMC said past reviews indicate that geotechnical issues are unknown and present a significant risk for application of LTCC in Australia. According to Terry Medhurst AMC principal geotechnical consultant, factors such as the effect of depth, differing stress regimes and coal strength, lump size and the flow characteristics of caved coal need to be quantified for predicting production rates.

One promising technique is the recently developed “Caving Simulator” known as CAVE-SIM. Developed by Glenn Sharrock of AMC, the key motivation for the development of CAVE-SIM is to properly simulate the effects that alternative extraction geometries and draw strategies would have on the economic performance of block cave and sub-level cave operations in hard rock mines.

CAVE-SIM is based on the cellular automata concept and models particle friction, particle size distributions and stress in 3D and can simulate interaction of large numbers of particles, greater than 30 million. The user has full control over draw rates from individual drawpoints and there is full tracking of the instantaneous grade and particle size distribution through each drawpoint.

The ability to model large numbers of particles also allows phenomena such as density segregation, arching, hang-ups and differential flow to emerge from the simulations. Overall, the ability to model long simulation times means that parametric studies on critical economic parameters such as cave rates and product mixing, and their influence on the draw profile are possible. These factors are critical to LTCC evaluations.

In conjunction with the gravity flow simulations, AMC has also developed in-house methods for evaluating cavability and associated longwall support load effects. The Ground Response Curve (GRC) concept allows ground behaviour and longwall support set-to-yield characteristics to be assessed together.

“The combined GRC/CAVE-SIM approach provides a unique ability to assess the full range of geotechnical issues associated with the LTCC method,” Medhurst said.