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Longwall Top Coal Caving (LTCC) is considered one of the most efficient methods for mining thick coal seams. Compared to other thick seam mining methods, LTCC can offer significantly reduced operational costs, high production and resource recovery rates, and improve mine safety. The successful technical application of LTCC is controlled by the understanding of geotechnical mechanisms associated with its operation (LTCC mechanisms) and by the reliable prediction of top coal cavability. However, current understanding of LTCC mechanisms is limited, thus restricting the validity of existing top coal cavability assessment criteria. The research contains investigations into the applicability evaluation of LTCC. The main objectives were (1) the development of an advanced numerical modelling approach for studying LTCC mechanisms; (2) the improvement of understanding of major LTCC mechanisms; (3) the evaluation of parameters that have important impacts on top coal cavability; and (4) the development of an advanced criterion for assessing top coal cavability. Numerical modelling method was used as the main tool for investigating LTCC mechanisms and evaluating critical parameters. Based on model results, statistical analysis and back analysis of LTCC practices were implemented in developing the proposed cavability assessment criterion. The most significant results of this research included (1) an advanced numerical modelling approach for studying LTCC problems; (2) improved understanding of stress redistribution, material failure, strata instability and roof strata movement associated with LTCC operation; and (3) an advanced assessment criterion for top coal cavability. The advanced numerical modelling approach is, for the first time, successful in incorporating plastic material into a discontinuum code (UDEC) for modelling LTCC problems. This approach is capable of explicitly representing caving, adequately capturing rock strength disintegration and sufficiently incorporating roof strata movement. The improved understanding of LTCC mechanisms assists engineers in better identifying and managing potential LTCC-associated geotechnical risks. The advanced cavability assessment criterion provides engineers with a more comprehensive and reliable tool to predict top coal cavability. The advanced criterion combined with improved understanding can be used in the coal industry for efficiently evaluating LTCC applicability at the feasibility stage of a new mining project. |
