Published in September 2006 Australian Longwall Magazine

Funded by the Australian Research Council with Ulan Coal Mine as the industry partner, the research work on LTCC technology is led by Professor Bruce Hebblewhite (UNSW).

The research team consists of Abouzar Vakili (UNSW), Dr. Yue Jun Cai (UNSW), Richard Van Laeren (Ulan) and Jillian Wright (Xstrata), with external assistance from Brett Poulsen (CSIRO).

The team began research work nearly a year ago and has since developed a detailed UDEC (Universal Distinct Element Code) model for geomechanical investigations and simulation of the LTCC method. The model can also be used for conventional longwall mining methods and has already been presented to Ulan coal mine deputies and received a positive reaction.

Vakili, a UNSW PhD student, said although the LTCC mining method has operated in China for many years, there are many unsolved issues pertaining to the method.

“In terms of geomechanics, cavability is the key issue that could cause many limitations for applicability of LTCC method in different sites around Australia,” he said.

There is a pressing need for a method of cavability prediction and assessment.

“Chinese miners use blasting in cases where the roof has undesirable caving conditions, however, due to safety issues, blasting is normally not permitted in Australian underground coal mines, and would greatly inhibit high productivity. As a result, there is a need for a complete study of roof cavability and the parameters, which could influence that.”

Interesting features of the model include fully dynamic movement of the support; simulation of hydraulic pressure of support; release and closure of the canopy flipper to draw the caved coal from the rear armoured face conveyor and rear AFC extraction of the caved coal.

In addition, the model has built-in monitoring tools for cavability assessment including Roof Average Vertical/Horizontal Displacement, calculation of top coal recovery rate, caving angle and chock pressure history.

The UDEC program employs a discontinuum method, and in cases where displacement is the key parameter for analysis, discontinuum analysis gives much more accurate results than traditional continuum methods, Vakili said.

Compared with continuum methods such as the finite element and finite difference method, discontinuum methods have the capability to model complete detachment and rotation of elements and accept high density of joints and bedding planes within the model.

“In situations like caving where high amounts of displacement occur and particles detach completely and joints are the controlling factor, the most reliable method would be the discontinuum methods.”

Another feature of the model is a Visual Basic user interface, which accelerates the generation of the model code for different site conditions and makes the controlling approaches faster and easier.

Modifying the parameters and geometry of the model without the interface is a difficult and time-consuming process, and the simplicity of the interface makes it easy for any user with an elementary knowledge of UDEC to conduct advanced analysis for LTCC or conventional coal mining.

The model will be aimed at the Australian market, however, because of the generality of the model, it could also be used by overseas LTCC operations and conventional longwall operations.

Adapting LTCC to Australian conditions could potentially double the recoverable amount of coal and offer significant reductions in mine operating costs. With the first ever Australian LTCC mine, Austar, scheduled to begin cutting coal in September this year, a new era in underground coal mining is set to begin.