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Subsidence Field Observations <br />West Elk Mine <br />August 27-29, 2002 <br />Compression features also occur above the mine panels where the ground surface is subject to <br />compression. These features, which occur towazd the center of the mining panel, look like small <br />anticlines or bulges. They often aze harder to distinguish than cracks, because they may be <br />masked by the soil, colluvium, and brush at the surface more than the cracks. <br />2.2 Construction Cracks <br />Construction cracks aze common on the banks of newly constructed roads. These cracks develop <br />during the process of cutting into a side slope with a bulldozer. The cracks aze most common <br />where fractured and weathered rock is encountered; however, fractures also occur in soil and <br />colluvium where roots and brush aze pulled up during construction activities. In contrast to <br />subsidence cracks, construction cracks form an irregulaz pattern and aze more a function of the <br />material in which the road is founded. For example, these cracks often form a continuous zone <br />of irregulaz cracks where weathered bedrock has been cut into with the bulldozer. <br />Construction cracks can be confused with subsidence cracks on occasion, particulazly where <br />local weathered bedrock is cut with the bulldozer, and where mining has occurred below. The <br />less regulaz crack pattem is the most diagnostic feature for determining whether they aze <br />subsidence cracks or construction cracks. Also transverse and longitudinal subsidence cracks <br />have a definite geometrical relationship to the longwall panel. <br />2.3 Desiccation Cracks <br />Desiccation cracks aze common in the clays and silts of the Wasatch and Mesaverde Formations <br />in the West Elk mine area. The process of desiccation involves the shrinking of clays and silts, <br />particulazly after a sudden dry spell following an extensive wet period. <br />Desiccation cracks can be recognized by their very irregulaz pattern. Some of the lazgest <br />desiccation cracks were observed in clays of the Mesaverde Formation in the Horse Gulch- <br />Minnesota Reservoir azea where no mining had been done. As with construction cracks, the <br />larger, more regulaz desiccation cracks maybe confused with subsidence cracks. However, <br />831-032.570 Wright Water Engineers, Inc. Page 4 <br />December 2002 <br />