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2005 Subsidence and Geologic Field Observations <br />Box Canyon, W est Flatiron, Apache Rocks, <br />and Sauth of Divitle Mining Areas <br />areas above gate roads with arigid-pillar configuration. The cracks may stay open or close in <br />areas above gate roads with a combination rigid-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 occur toward the center of the mining panel in zones of maximum compression, <br />are usually more difficult to recognize. They often are masked, or absorbed, by soil and <br />colluvium, or are hidden in the brush and grass. They also may be indistinguishable from natural <br />humps and mounds in the soil and colluvium. <br />2.2 Construction Cracks <br />Cracks caused by construction activities are common on the banks of newly constructed roads <br />and drill pads. These cracks are often caused by the bulldozer during construction activities. The <br />cracks are most noticeable where fractured and weathered bedrock is encountered during <br />excavation. However, this type of cracking also occurs in soil and colluvium where roots of <br />brush and trees are pulled out of the road cut by the bulldozer. in contrast to subsidence cracks, <br />construction cracks occur in a rather continuous zone where weathered and/or Fractured bedrock <br />has been cut through, or where brush and trees have been pulled out of soil and/or colluvium. <br />The most diagnostic difference between subsidence cracks and construction cracks is that the <br />construction cracks 1) have a less regular pattern, 2) are related to the material they occur in, and <br />3) lack any spatial crack 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 area where the rocks are weathered to clays and silts. The <br />process of desiccation involves the shrinking of the clays and silts after a dry period that follows <br />a wet period, when the material swells (i.e., the shrink/swell process). <br />831-032.710 Wright Water Engineers, Inc. Page 5 <br />November 2005 <br />