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No. 6 Mine longwall under No. 5 Mine longwall -The total amount of subsidence for a surface point <br />from both episodes of longwall mining is simply [he sum of the subsidence resulting from each individual <br />mining episode. <br />• No. 6 Mine longwall under No. 5 Mine room-and-pillaz workings- The principles of superposition were <br />applied. The subsidence contribution from the No. 6 Mine longwall was calculated with the zone area <br />computer model. The subsidence from the No. 5 Mine room-and-pillar areas were calculated utilizing the <br />Lee and Abel (1980) equation: <br />Subsidence (SUB) % = 8.469 + 11.95 [In(LMAX(m/Pw))] <br />Where: <br />SUB% =Subsidence as a percent of mining height <br />LMAX = Kh/(1-R) <br />K = 0.0226 MPa per meter of depth <br />h =overburden height (meters) <br />R =extraction ratio <br />M =mining height (meters) <br />Pw =pillar width (meters) <br />This equation is based on the fact that as pillars fail, they crush and expand but do not flatten out uniformly. The <br />shortened and crushed pillars increase in load carrying capacity in some proportion to their increase in cross-section <br />area. It should be noted that the Lee and Abel equation yields subsidence predictions within two (2) percent of the <br />actual observed subsidence from the room-and-pillar panels at the EC Mine for overburden depths greater than 400 <br />feet. <br />Predicted Maximum Subsidence. Subsidence in the permit area is predicted to be 60 to 65 percent of the extracted <br />mining height. The projected typical subsidence contours for longwall panels is presented on Figure 60, Subsidence <br />Contours -Five Year Mining. These predicted surface subsidence phenomena were developed from the information <br />presented earlier in this section. <br />It was assumed for this evaluation that the average extraction height for longwall mining would be 12 fee[, In <br />addition, it was assumed [hat the headgate and tailgate chain pillars would fail and crush when panels on both sides <br />had been mined. A key assumption in this analysis is that similar geologic and topographic environments will subside <br />in a similar manner. This assumption allowed subsidence data collected throughout the EC Mine complex to be <br />applied to this analysis. A summary of the maximum predicted subsidence for each of the typical mining geometry's <br />on Table 84, Maximum Predicted Subsidence for Typical Mining Geometry's. <br />Overburden Subsidence Effects. The effects of subsidence are distributed throughout the entire overburden section. <br />The effects of subsidence in the overburden are of importance because they may effect water-beazing characteristics of <br />the overburden strata. Overburden effects are broadly grouped into the four-(4) zones shown on Figure 61, <br />Distribution of Subsidence Effects and Overburden. The four {4) zones are as follows: <br />• Zone 4 -Near Surface Fissuring <br />• Zone 3 -Minimally Affected Overburden <br />• Zone 2 -Possible Bed Separation <br />• Zone 1 -Caving and Heavy Fracturing <br />The formation of these zones is dependent on a variety of factors including 1) the depth of cover, 2) capability of the <br />near-roof strata, and 3) the strength of the overburden strata. The thickness of each zone is dependent upon the <br />characteristic of the overburden section. <br />Permit Revision 04-34 2.05-60 Revised 7/2/04 <br />