Design Optimization of Longwall Chain Pillars

Determination of the optimum design of chain pillars has a significant effect on the economics and safety of Longwall operations. Most pillar design formulae are based on empirical methods with supplemented by local experience. They therefore lack versatility of application under different geotechnical conditions. In this paper, in order to illustrate the shortcomings of the above, a typical real coal pillar in Tabas coal mine has first been studied and the conventional formulae have been used to determine the optimum dimensions. The results show that a wide difference exists between the predicted and the real field data. The Oraee-Hosseini formula has then been applied to this mine in order to determine the optimum design. The results from this formula demonstrate a close fit between the theoretical values and those produced by laboratory tests and in practice. It is further demonstrated that the wide discrepancy between the results obtained from the two formulae is attributed to the dissimilarities between geotechnical conditions of Tabas and the original regions whose data were used to devise the empirical formulae. It is finally concluded that the application of numerical simulation methods and experimental equations together with engineering judgment used by the mining design engineer, will provide the most accurate design characteristics