Numerical Modelling of Mining Induced Subsidence in Areas of High Topographic Relief, the paper presented by University of Wollongong researchers Walter Keilich, Naj Aziz and Ernest Baafi, looks at the issue of ground subsidence due to mining. The subject of research for several decades, it remains an important topic confronting the mining industry today.

In this project, a methodology of subsidence prediction using the universal distinct element code (UDEC) has been developed as an alternative for subsidence modelling in the Southern Coalfields. The UDEC model has been validated by comparison with empirical results, the application of the Voussoir beam method and comparison of observed caving behaviour. It is anticipated that the methodology will be applied to real case studies for further verification.

The aim of this project is to develop a model that can be used to assess subsidence impacts on undermined river valleys. The developed methodology is expected to be a true predictor of subsidence and would provide reliable subsidence predictions for a range of mining geometries in the same geological environment. The expected outcomes will include a reliable subsidence prediction tool capable of simulating ground deformations and subsurface movements in flat terrain and river valleys.

The paper by SCT Operations geotechnical engineer Justine Calleja, Rapid Rating – Using Coal Mine Roof Rating to Provide Rapid Mine Roof Characterisation from Exploration Drilling, looks at a new method for calculating the coal mine roof rating (CMRR).

“Rapid Rating” has been designed to allow large quantities of exploration data to be processed quickly to provide a standardised indicator of geotechnical conditions and is intended to make CMRR more readily available to mine operators.

The need to assess large quantities of drill core in very short time frames has only emerged relatively recently, and Rapid Rating has been developed to meet this need. Rapid Rating can calculate CMRR over numerous possible bolt lengths for sensitivity studies on different bolting horizons and during the early stages of mine design when bolt length is still a variable. The Rapid Rating calculation method is automated, which makes the results more repeatable and less subjective.

SCT Operations project leader Dr Winton Gale will present Computer Modelling of Water and Gas Flow about Longwall Panels, which relates the current state of modelling of rock fracture and fluid flow using fully coupled mechanical and two-phase flow routines. The results presented relate to work conducted within recent and current ACARP studies of water inflow and the gas desorption effects of coal.

The paper relates the impact of mining on the ground permeability and changes to the hydrological regime. Mining impacts on the overburden and surface aquifers are discussed. The impact of mining on gas desorption and migration to the extraction panels is discussed with reference to coal gas sources below and also above the mined seam.

Development of an Integrated Real-time Roof Monitoring System will be presented by CSIRO Exploration and Mining geotechnical engineers Baotang Shen and Hua Guo and geophysicist Andrew King, outlining a real-time roof monitoring and warning system for underground coal mines.

CSIRO has been conducting a five-year research project under the sponsorship of the Japan Coal Energy Center (JCOAL) and Ulan Mine to develop the system. A preliminary system has been developed and successfully trialled twice in the gateroads at Ulan Mine during 2004 and 2005. The system integrates the displacement monitoring, stress monitoring and seismic monitoring in one package and includes GEL multi-anchor extensometers, vibrating wire uniaxial stress meters, and an ESG seismic monitoring system with microseismic sensors and high frequency AE sensors.

The trials of the system in two tailgates at Ulan Mine have demonstrated that the system is effective to monitor the behaviour and stability of the roadways during longwall mining. The continuous roof displacement/stress data have shown clear precursors of roof falls. The seismic data (event count and locations) have provided insights into the roof failure process during roof falls.

A fifth paper, Effect of Grouting on Longwall Mining through Faults, to be presented by Terry Medhurst and Michael Bartlett of AMC Consultants, presents a recent ACARP project that assessed faulted areas to determine the need for grouting and its impact on mining performance.

The paper includes a comparative analysis of theoretical grouting assessment and empirical results from several mines. The outcomes are directed to assist operators in understanding when fault grouting is required, how it might be implemented and expected outcomes of the grouting program.

The conference is on July 5-7 at the University of Wollongong and is being organised by the Illawarra Branch of the Australasian Institute of Mining and Metallurgy in conjunction with UOW and Mine Managers Association of Australia.