2025-05-05_PERMIT FILE - C1981010 (32)

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Tonia Perkins July 31, 2024 Page 11 Agapito Associates, Inc. Table 1. Geometric Parameters from Empirical Designs Applied in Numerical Models LaModel Analysis The LaModel figures presented in this report provide plan-view representations of the vertical stresses and safety factors of the pillars for a variety of scenarios. The vertical stress plots illustrate the anticipated stress environment, while the safety factor plots show that the web and barrier pillars satisfy the design criteria under the base set of conditions and provide sufficient loading capacity when one or more nearby pillars fail. Confirmation of Design and Analysis of Seam Interaction Effects LaModel results showing basic design performance are shown in Figures 4 and 5 for the M and Q seams, respectively, on the North side of the N-Pit. Figures 6 and 7 show results for the M and Q seams on the South side of the N-Pit. The (a) portion of each figure shows the vertical stress distribution in units of psi, and the (b) portion shows the safety factors. The web pillars satisfy the minimum safety factor of 1.6 for the design criteria in both seams. Interaction is minimal between the M and Q seams. Although the web pillars support the highest stress magnitudes on the M Seam, there is no visual evidence of these stress concentrations being transmitted to the Q Seam below. Refer to Figure 5 for contours of the vertical stress in the North Q Seam. Evidence of multi-seam interaction in this scenario would be noted by angled patterns in the stress contours, since the North M Seam excavations are oriented approximately 13 degrees from normal to the pit slope. Cascading Pillar Failure Analysis Cascading pillar failures can occur when failure in one pillar results in stress transfer to adjacent pillars, which, in turn, fail. In their mildest form (slow pillar squeezes), this failure may take weeks to progress. In their most severe form, failures can occur almost instantaneously, resulting in severe air blasts, damage to equipment, and loss of life. To check the performance of the web pillar designs against cascading pillar failure, additional LaModel analyses were run. In these models, Empirical Design (ft)LaModel (ft)Flac3D (ft) Depth of cover 170 170 varies Seam height 6 6 6 Entry width 11.5 12 12 Web pillars 6 6 6 Barrier pillars 18.3 18 18 Depth of cover 210 210 varies Seam height 11 11 12 Entry width 11.5 12 12 Web pillars 8.8 9 9 Barrier pillars 29.4 30 30 M Seam Q Seam