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Subsidence Field Observations <br />West Elk Mine <br />July 22-24, 2003 <br />azeas above gate roads with a combination rigid-pillaz/yield-pillar configuration (for example, the <br />head gate entries of longwall Panels 15 and 17 have arigid-pillar/yield-pillar configuration). <br />Compression features (bulges and warps) also occur above the longwall mining panels in areas <br />where the ground surface undergoes compression in the subsidence process. The compression <br />features, which typically occur towazd the center of the mining panel in zones of maximum <br />compression, aze usually more difficult to determine, because they often are masked, or absorbed, <br />by soil and colluvium, or are hidden in the brush and grass. They also may be indistinguishable <br />from natural humps and mounds in the soil and colluvium. <br />2.2 Construction Cracks <br />Cracks caused by construction activities aze common on the banks of newly constructed roads. <br />These cracks are caused by the cutting of the road cuts by a bulldozer, for example. The cracks <br />aze most noticeable where fractured and weathered bedrock is encountered; however, this type of <br />cracking also occurs in soil and colluvium where roots of brush and trees are pulled out of the <br />road cut by the bulldozer. In contrast to subsidence cracks, construction cracks occur in a <br />continuous zone where weathered and/or fractured bedrock has been cut through, or where brush <br />and trees have been pulled out of soil and/or colluvium. <br />Construction cracks may be confused with subsidence cracks, particularly where mining has <br />occurred in the area, and where local bedrock is weathered and fractured, or where brush and <br />trees have been ripped out of soil and/or colluvium during the construction process. The most <br />diagnostic features of construction cracks are their less regular pattern, relation to the material <br />they occur in, and lack of any spatial relationship to the longwall mining geometry. <br />2.3 Desiccation Cracks <br />Desiccation cracks tend to occur in claystones and siltstones of the Mesaverde and Wasatch <br />Formations in the West Elk Mine azea, particularly where the rocks are weathered to clays and <br />831-032.610 Wright Water Engineers, Inc. Page 4 <br />September 2003 <br />