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1.8 POSSIBLE SUBSIDENCE IMPLICATIONS OF FAULTS <br />A study done by Dames & Moore (1981) reported that the Orchard Valley Mine <br />(Bowie #1 Mine) experienced roof control problems in the worKings mined parallel and <br />adjacent to the "Section 13 fault". The caving was reported as conical shaped and up to <br />10 feet wide, with slickensides present that seemed to bound the cone and that probably <br />acted as the planes of weakness for the caving. There was no mention in the report of any <br />surface effects associated with the mining adjacent to the fault. <br />In predicting the effects faults have on chimney collapse, it is conceivable that a <br />significant failure of this type has the potential to breach the surface and darnage <br />structures and renewable resources. There is potential that a highly fractured fault could <br />contain goaf with an extremely low swell ratio so that void caused by the failure is not filled <br />as quickly as predicted for the material evaluated in section 1.7 of this Exhibit. Although <br />no precedence is known for this prediction, an analysis is done using an extremely <br />conservative approach. <br />An analysis is made for Mains entries, at a mining height of 9.5 feet, crossing <br />through the fault trace shown on Map No. 27. The assumptions made for this analysis are; <br />1) the width of the fracture zone is at least 20 feet wide and centered over one of the <br />development openings (thus the worst-case conical chimney height prediction method can <br />be used as shown in section 1.7 of this Exhibit), and; 2) the roof rock material present <br />within or adjacent to the fault exhibits bulking or swell properties common to sand (%S = <br />10%). This evaluation predicts that the worst-case conical chimney collapse should not <br />breach more than 285 feet of overburden. <br />Little is known of any other subsidence implications of faults in underground coal <br />mining. A paper by A. J. Lee (1966) gives results of an analysis and tentative rules for the <br />prediction of movement of faults present in mining areas. The author chose a fifteen <br />square mile area, southeast of Barnsley, England, where 35 faults where extensively <br />mapped and studied. The analysis indicated that it is more likely that a step will be <br />observed at the surface when; 1) the coal is mined out beneath the fault plane; 2) the <br />surface trace of the fault lies 1/5 the depth over the mined out area and; 3) the fault step <br />height is roughly 1/3 of the maximum predicted subsidence. <br /> <br />- 16 - 10/00 <br />PR-o y <br />