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• <br />Figure lb presents the planned mining geometries and the location of detailed models. Mining <br />geometry includes the set of mains being driven under the drainage, the storage panel and three <br />longwall panels in both the Upper D and the Upper B Seams. For clarity the Upper D Seam <br />workings are excluded from the Figures. <br />Table 2 presents the scope of the modeling. Isolated development conditions are analyzed in step <br />1. By simulating the longwall retreat in the neighboring district, load transfer toward the corridor <br />is conservatively estimated in step 2. <br />Table 2 —Scone of boundary- element modeling <br />Analyses Seam Comment <br />1- Development B and D Two seam development <br />2- Retreat B and D Load transfer from longwalls <br />2.2 Results • <br />Modeling results are presented as vertical stress and factor of safety levels (Figures 2 and 3). In <br />Figure 2, square elements are 18- by 18- by 9.5 -ft coal elements, the color of which depends on <br />the stresses acting on them. Figure 3 presents the factor of safety for each element. The factor of <br />safety is based on the pillar strength which is calculated using Mark - Bieniaswki formula (Mark <br />and Chase 1997). This equation depends on the pillar dimensions and the excavation height. For <br />clarity, only the results from the northern end of the model are presented. <br />Clearly vertical stress concentration is influenced by variations in overburden thickness and is <br />mostly low to moderate ( <1,500 psi) directly beneath Terror Creek, even after considering <br />simulated longwall load transfer. The minimum average pillar factor -of- safety for the mains <br />exceeds 3.0 directly under the creek for simulated development mining using the 900 psi coal <br />strength suggested by NIOSH. Using a more conservative coal strength value of 600 psi, <br />commonly used by BRL for very week geologic conditions encountered in portions of <br />neighboring longwalls (Stewart 2009), the minimum average pillar factor -of- safety for the mains is <br />Maleki Technologies, Inc. Page 4 <br />