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Page 28 <br />The subsidence prediction program integrates over the azea of mining to determine the <br />„ ~ maximum possible surface subsidence using an influence function. A material property required <br />for the analysis is the angle of draw. For the influence function, we have used a normal distribu- <br />lion function which has been used for many yeazs to predict mine subsidence in the United States <br />and elsewhere -see, for example, SME Handbook Chapter 10.6. <br />An angle of draw of 45° was assumed based on the soft overburden in the immediate vi- <br />tinily of mining. Above the A-Groove, the material might be considered hazd/strong, resulting <br />in a lower overall angle of draw. The maximum possible subsidence was conservatively as- <br />signed as 100% of the extraction height. Experience from coal mining indicates that a reduction <br />factor of 60% to 80% generally yields satisfactory prediction. <br />Figure 5-9 shows the predicted surface subsidence induced from the mined area for <br />Phases I and II of the mine plane. The maximum possible subsidence is approximately 10 ft. <br />This analysis using the influence function method, indicates a higher possible subsidence than <br />the eazlier analysis (shown in Figure 5-7). Bulking of the insolubles in the zone of dissolution <br />(LBB to the dissolution surface) and bulking of the caved material above the solution cavern will <br />~~ reduce the total subsidence from that predicted and shown in Figure 5-9; hence, the subsidence is <br />estimated to be between 3 and 10 ft. <br />~ '1 <br />Agapito Associates, Inc. -- <br />