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A Case Study of Topography–Related Stress Rotation Effects on Multi–seam Stability
33rd International Conference on Ground Control in Mining
A Case Study of Topography–Related Stress Rotation Effects on Multi–seam Stability
by
Ihsan Berk TuluTed KlemettiEssie Esterhuizen, NIOSH, Office of Mine Safety and Health Research, Pittsburgh, United StatesJames Sumner, Lone Mountain Processing Inc., St. Charles, United States
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[Conference] 33rd International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Stress assessment studies
[Author] Ihsan Berk TuluTed KlemettiEssie Esterhuizen, NIOSH, Office of Mine Safety and Health Research, Pittsburgh, United StatesJames Sumner, Lone Mountain Processing Inc., St. Charles, United States
[Abstract] 
Key Conclusions:
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Consequently the layout was changed in the L-5 panel by moving the number 5 entry 30 ft away from its originally planned position, so that it would be located in more favorable stress. At the time of writing this paper, the conditions in the number 5 entry of the L-5 panel are significantly better than experienced during mining of the L-6 panel.
Key Findings:
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In order to investigate the contradictory observation, a site visit was made, ground conditions were observed, and stress mapping was conducted. Major and minor horizontal stress directions were generated from the stress mapping. Possible effects of multiple seam mining were investigated with the Analysis of Multiple Seam Mining (AMSS) software. Neither the field observations nor the empirical understanding of horizontal stress effects nor the AMSS results could explain the observed damage. A 2D Finite element analysis was conducted to determine whether there were any unexpected interactions related to the combined effect of horizontal and vertical stress. Based on this detailed investigation, it was discovered that the topography results in rotation of the major stress. The stress rotation causes asymmetrical interactions between the seams which can explain the unexpected response observed in the mine.
Objective of the Paper:
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The mine is located in Harlan County, Kentucky. It is a multiple seam room and pillar mine. The topography is highly variable and the depth of cover varies between 300 and 2,000 ft. In this mine, L-6 panel developed with five entries into the Kellioka seam is accessed via an in-mine slope from the overlying Darby seam workings. This panel is overlain by mined out panels in the overlying Darby and Owl seams. Favorable conditions were expected because the Kellioka seam development was thought to be located within the stress shadow of the Darby panel. The L-6 panel was experiencing roof damage in the number 5 entry due to horizontal stress. However, based on the current understanding of horizontal stress effects, roof damage was expected to be located in the number 1 entry. There was concern about the safety of mining the adjacent L-5 panel, which was the next panel to be mined.
Problem Statement:
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In general, theoretical and empirical knowledge regarding the impact of horizontal stress on underground coal mining is fairly well understood. Multi-seam interactions are generally evaluated by considering vertical stress changes caused by mining in over- or underlying seams. Recently, the Office of Mine Safety and Health Research (OMSHR) investigated a multi-seam stability problem in a central Appalachian mine where it was found that both the horizontal stress and the vertical stress were influenced by the topography causing unexpected difficult ground conditions.