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• 1.0 INTRODOCTION AND SOM,MARY <br />Tliis report examines the potential for subsidence from full <br />extraction, room and pillar mining at the Bear Mine No. 3 at <br />Somerset, Colorado. It further examines the probable effects of <br />the subsidence on existing landslides and on the potential for <br />the creation of new slides. The study concludes that subsidence <br />will have both short-term and long-term effects on the potential <br />for reactivation of old slides as well as the development of new <br />slides. Short-term effects include the development of tension <br />cracks at the surface in zones within the subsidence profile that <br />experience a tensile ground strain. These tensile zones will <br />temporari ly alter the state of stress in the adjacent soi 1 and <br />• rock and increase the amount of moisture entering the subsurface <br />during a given storm event. Relatively minor movements would, <br />however, result in quickly regaining the original state of stress <br />within the tensile zones. Further, the effects on surface and <br />subsurface drainage would diminish as surface tension cracks <br />began to heal. <br />Long-term effects include the rubblization of rock in the <br />immediate roof area and for some distance above the mine level <br />permanently altering the shear strength characteristics of those <br />materials in the geologic profile. In areas of low overburden <br />thickness where chimney subsidence might result in the <br />. development of sinkholes on the surface, a permanent surface <br />drainage modification might result which would increase <br />1 <br />