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SubTerra, Inc. Peabody Twentymile Coal, LLC 03/16/2015 <br />Foidel Creek Mine <br />Permit Revision for Longwall Mining in the Wolf Creek Seam - Subsidence Evaluation <br />2. Mine Subsidence <br />2.1. Subsidence Mechanics <br />Although an extensive review of subsidence mechanics is beyond the scope of this report, it is <br />appropriate to present an understanding of the way in which the void created by longwall mining is <br />transmitted to the surface. In general, as a longwall face retreats, the immediate roof strata <br />separate at bedding planes and pre-existing sub -vertical discontinuities and cave behind the face <br />supports. Caving propagates until it is arrested through bulking and/or intersection with more <br />competent overlying beds. As the longwall face retreats further beyond the section, the overlying <br />beds fail in bending and deform towards the centroid of the excavation ultimately resulting in <br />subsidence at the ground surface. During this deformation, shearing occurs along bedding planes <br />and bed separation occurs where more competent strata overly less competent members. These <br />actions affect both the limit and magnitude of subsidence that is transmitted to the surface. <br />The layout of development entries and the size of headgate and tailgate pillars also influence the <br />shape of the final transverse subsidence curve and related deformations (tilt, curvature, and strain) <br />both in single and subsequent panel mining. Figure 1 illustrates the change in vertical stress and <br />deformations that occur during entry development and longwall mining and the resulting zones of <br />horizontal extension and compression at the ground surface. <br />Panel <br />Ribside <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />Vertical Stress I <br />Redistribution <br />/ I <br />YieldR gid" or <br />Pillar Abutment <br />Pillar <br />(a) After Development <br />+E <br />Sq <br />Ftvure 1 <br />Generalized �.,ertical Stt-e,;s Change and <br />Ditiplat•ement during Longwall Relining <br />(llerr e:1 imrig, ml�a-matton torn Mark. 191)2 <br />B!ena s}.l, <br />1J9-1 Sh<! IbviL ly 71 <br />Panel Panel <br />Strain <br />Curve , Extension Compression <br />o _ <br />Subsidence �I <br />Curve <br />I I <br />I I <br />Zone of Vertical Extension <br />I (bed separation) <br />I I <br />L too <br />0 zone of Bed separation <br />/o <br />01 Zone of caving / <br />Pillar Yield and Floor <br />Punching Floor Heave Zane of Incomplete <br />(load iransferto cure) Convergence <br />(b) After Longwall Extraction (c) Zones of Fracturing <br />(Singh. 1986) <br />EXPLANATION: <br />M Extracted seam t ckness <br />S = Subsidence <br />(Tv = in-situ vertcal stress <br />appp = Side abutment stress <br />+E Extension <br />-E = Compression <br />3 PN: 2013-26 <br />