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Abstract: The conventional deterministic approach based (DAB) methods are simple and widely used to determine an adequate chain pillar size in coal mines where geological settings, coal characterizations and mining methods have been explored. It is evident that such deterministic methods have some intrinsic limitations in handling uncertainties in material properties, non-regular geometries and different mining operations. In the deterministic stability analysis of a chain pillar, the safety factors as well as all input parameters are deterministic. Although, these parameters generally exhibit uncertainty and should lead to a probabilistic expression for the safety factor. The probabilistic analysis provides a confidence interval to express the reliability of chain pillars stability. In this paper, safety factor is defined as a probabilistic function and the failure probability of designed chain pillar of Tabas coal mine is then evaluated using the First Order Second Moment (FOSM) and the Advanced Second Moment (ASM) methods. The results of the probabilistic stability analysis show that the confidence interval for designed pillars with both mentioned methods applied are similar and their values vary from 84% to 88%. The results of such analyses can be used as a basis for decision-making about the size of chain pillars and reduce the risk of pillars stability as well as the uncertainties. However, a trade-off between cost is essential for making the final decision. [Copyright &y& Elsevier]

Abstract: Longwall mining is a common mining method in Iran that is often affected by out-of-seam dilution (OSD). The field investigations performed in Tabas coal mine show that OSD often occurs due to roof falls in front of the face area before support setting and also removing some floor material. The increase in unsupported roof span above the shearer may cause difficulty in controlling the roof and consequently increases dilution of the run of mine (ROM) coal. The paper presents the results of a study on some dominant factors causing OSD in prop-free front of the face in longwall retreat mining method. A series of two-dimensional numerical models are developed and analyzed to examine the effects of mining depth, in-situ stress, unsupported roof geometry above the shearer as well as roof and floor strata quality and dip of coal seam on OSD. Two criteria were established, one considers the roof falls, defined as low stress level or plasticity zones under yield tension which roof material unravels and other is about removing floor, defined as depth of support and shearer sinking into the floor. The equivalent linear relaxation depth (ELRD) and depth of removing floor (DRF) concepts were used to quantify OSD. The methodology presented in this study is useful since it can be applied to develop mine-specific design tools for the prediction of OSD. [Copyright &y& Elsevier]