Coal Age

APR 2013

Coal Age Magazine - For nearly 100 years, Coal Age has been the magazine that readers can trust for guidance and insight on this important industry.

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roof control continued shape and extension of failed zones differ slightly. Coal ribs mostly fail due to tensile stress, while roof and floor strata fail primarily due to shear stresses. Rib corners fail due to a combination of shear and tensile stresses. The peak values for each SCF are located around the edge of the opening or pillar, 0.5-ft into the entry or pillar. The vertical SCF values for a 4-way intersection are higher than a 3-way intersection (about 7% to 32% along different cross-sections) but it occurs deeper into the solid pillar. Both HSCFX and -Y value for a 3-way intersection are higher than the 4-way intersection. Thus, a 4-way intersection provides better stability for horizontal stress. The peak VSCF and HSCF values for pillar with 120° angle crosscut occur into the opening that makes this pillar more vulnerable from ground control point of view. Supplementary support might be required near this pillar. Effective pillar off-set distance for 3-way intersection design is critical. It is important to identify the minimum off-set distance value, which would be required to prevent the 52 www.coalage.com Figure 2: Failed zone for a 3-way intersection with a 25-ft off-set. overlap of stress concentration zones created by the two side-by-side intersections. In this study a 3-way intersection with 45-ft off-set provides better stability and decreases the span of failed zone. Identifying the height of the failed zone is critical for designing an appropriate support system such as cable bolt, truss system, torque-tension bolt system, etc. For more information on this research program, contact SME (www.smenet.org). Ask for Pre-Print 13-148, Numerical Analyes of Stability of 3-way and 4-way Coal Mine Intersection in Illinois by B. Abbasi, SIU-Carbondale, and Y.P. Chugh, SIU-Carbondale. April 2013

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