ABSTRACT: The paper presents a numerical modelling approach by discontinuum method to simulate the progressive caving of top coal and roof above a Longwall Top Coal Caving (LTCC) face in Bowen basin, Queensland, Australia. A new caving modelling approach has been developed by the application of strainsoftening material model within UDEC in order to represent the failure and caving induced by the mining process. Results of numerical simulation have improved the understanding on LTCC mechanisms in terms of stress redistribution, rupture mode and failure mechanism in coal and roof strata. These results are in general agreement with site observation and previous longwall studies.
Longwall Top Coal Caving (LTCC) is an improved longwall mining technique that has shown many advantages compared with other methods in terms of coal recovery rate, face equipment design, development cost and spontaneous combustion control for extracting coal seam with thickness in excess of 4.5 m (Hebblewhite et al. 2002). Regarding the geotechnical issues, the applicability of LTCC is believed to highly depend on the cavability of top coal. The presence of top coal as a weak and highly jointed roof rock combined with the higher caving height (Fig. 1) makes the roof caving mechanism different from that caused by conventional longwall mining. Numerical modelling has been widely applied in LTCC studies due to its potential to represent the multiple caving mechanisms under various mining conditions. However, for continuum methods, the models have been limited to implicitly simulating the caving. The discontinuum methods, on the other hand, have mostly used the elastic model for intact rock and thus did not fully represent the failure behavior during caving. This paper aims to improve the understanding of mechanisms associated with caving by developing a discontinuous modelling approach using UDEC strain-softening model (Itasca Consulting Group 2014). The developed model is not only able to explicitly simulate the progressive caving but is also able to incorporate the plastic material response.