GENERAL30772 - Laserfiche WebLink

Home Browse Search

Subsidence is influenced by both the mining system and the geology. The lithology of the formation above a coal seam together with the bed thicknesses, bedding, cross-joint frequency and faults all control subsidence. Studies of the effect of faults on subsidence indicates that faults and fractures offer good sliding surfaces that can influence the angle of draw. A comprehensive geological investi- gation, including fault mapping and satellite imagery plotting, was conducted in the permit area (see geological section). This study failed to detect any faults or major fracture zones. The Staley Gordon Mine, abandoned in 1970, was mined using the room and pillar method. There is no detected subsidence above the abandoned mine although the overburden thickness is less than 200 feet and there are large caved areas in the abandoned mine. This indicates that the subsidence caused by small room and pillar sections will have minimal visual impact on the surface. However, the subsidence caused by the abandoned Staley Gordon Mine cannot be compared to the expected subsidence of the Deserado Mine because of its much larger scale of coal extraction. The highest recovery in caved pillar robbing areas of the Staley Gordon Mine was determined from the mine map to be approximately 68%. To calculate the maximum predicted surface subsidence and strain, a more conservative recovery of 75% was used. Using the actual depth of 300 feet at this location and a mining height of 6 feet, a maximum tensile strain of approximately 1700 micro-strains should be produced. This amount of tensile strain probably caused some surface cracks to open up. Since the mining and subsequent subsidence occurred more than ten years ago, normal weathering of the surface would have erased any surface cracking or other visible evidence of subsidence. This has in fact been found to be true; a visual inspection of the surface over the caved areas showed no surface cracks, tilted trees or other indicationsthat subsidence had even occurred. Significantsurfacesubsidence, as much as 7.7 feet for longwall mining and 0.5 feet for room and pillar mining, is predicted for the Deserado Mine. The long-term subsidence associated with time-dependent deterioration of pillar strength is predicted to be minor. Predicted horizontal tensile strains will probably result in development of surface cracks in the vicinity of the mining section. I.A.6.c Subsidence Prevention. BME utilizes a mining system that includes a subsidence control plan which will minimize damage and lessening value and use of the surface lands. The measures used in the mine to reduce the likelihood of subsidence damage besides longwall mining and full pillar extraction includethe following: Rio Blanco County Special Use Permitg8l-1 Exhibit B -Mining Plan Septem ber2000 9