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SubTerra, Inc. Peabody Twentymile Coal LLC 09/27/2014 <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 parcel 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 />Rib5de <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />Vartica€ Stress I <br />R ®- <br />distribution I <br />f <br />I <br />Yield "Rigid "or <br />Pillar Abutment <br />Pillar <br />(a) After Development <br />Figure I <br />Generalized Vertical Stress Change and <br />Displacement during Longwall Alining <br />IDerived using inrurnzation from Mark, 1992. <br />Bienawski, 1992, Shadbult_ 1977) <br />Panel <br />q <br />I <br />i <br />Pillar Yield and Floor X <br />Punchin <br />(load iransterto cure) Floor Heave <br />(b) After Longwall Extraction <br />Parml <br />Extension Compression <br />1�� I <br />l <br />I � <br />Zone of Vertical Extension I <br />(bed separation) I <br />I <br />� I <br />Zone of Bed Separation <br />01 Zone of Caving / <br />QQ 3 5m <br />I <br />Zone of Incomplete <br />Convergence <br />(e) Zones of Fracturing <br />(Singh, 1986) <br />EXPLANATION: <br />nl = Extractad seam thickness <br />S = Subsidence <br />cry = In -situ rerticat stress <br />T = Sida abul.ero stress <br />= Extension <br />-E = Compression <br />3 PN: 2013 -26 <br />