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The LGM model, a 3-D numerical model, based on a laminated medium used in conjunction with boundary element technique, was developed to simultaneously analyze both surface subsidence and in-mine stability of mine workings including roof-pillar-floor interaction. However, the model is not yet sufficiently user-friendly to promote its use by industry, and its use requires an in-depth understanding of the model and the parameters needed to create the datafile. This paper focuses on development of a simplified model that can estimate chain pillar loads for weak floor conditions based on LGM simulation results.
Meanwhile, based on the thickness and the modulus of elasticity of weak floor strata, the developed models estimate Bearing Capacity (UBC) of weak floor strata. It also accounts the effect of adjacent pillar on the UBC of weak floor strata. The model has been validated for Illinois Coal Basin seams that are typically underlain by weak floor.
The longwall gate entries are the lifeline of a coal mine. Improved longwall performance requires stable gate entries that provide safe access to the longwall face. Generally, the headgate entries must remain unobstructed and completely open, with minimum convergence to accommodate personnel, equipment and coal transportation. The tailgates, however, are mainly used for return and, sometimes, for intake air passages and travelways. Nevertheless, the gate entries are the most hazardous areas in longwall mines. Developing a comprehensive and practical gate entries by considering coal pillar size, mine roof quality and artificial support is a challenging task for the coal scientist and mine engineer. Past research regarding conventional chain pillar design based on coal strength is founded on either empirical or analytical approaches [1,2,3,4]. Except for the ALPS model, none of the other models is simple enough to facilitate industrial use. In the Illinois Coal Basin, coal seams are typically underlain by weak floor strata— a condition that makes floor bearing capacity a critical factor in chain pillar design but that is not included in the ALPS model, therefore, the ALPS model does not appear to provide very good first approximations of the pillar size required for gate entry stability in the Illinois Coal Basin coal seams. Recently, researchers at Southern Illinois University developed a numerical model (LGM model) for longwall pillar design that incorporates surface subsidence prediction as well as pillar load estimates and pillar settlement (Yang and Chugh,1993)[5,6].
The LGM model, a 3-D numerical model based on a laminated medium used in conjunction with a boundary element technique, was developed to simulate ground movements due to coal mining [7]. The results obtained with the LGM model were reasonable. Recently, this model was modified to simultaneously analyze both surface subsidence and in-mine stability of mine workings, including roof- pillar-floor interaction [6]. In this model, linear and nonlinear material behavior can be incorporated for coal pillar and floor strata, while overburden strata are treated as linear elastic material. Caved gob in a panel is modelled using a suitable non-linear material behavior.
