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L J <br />2.2 Calibration Methods <br />Historical mining experience was used to validate both the input <br />data and the pillar design model. The model and the design <br />values were used to calculate safety factors for various known <br />pillar geometries and response patterns. <br />As an example of these analyses, pillars in the 1st North Mains <br />were analyzed. Conversations with Link Derick (1991, personal <br />communication) indicated that the pillar response in this areas <br />was characterized by rib sloughage and sever floor heave. The <br />rib sloughage indicates that the pillars had a well developed, <br />destressed rib side zone. The floor heave indicates the pillars <br />were sized such that they carried large loads rather than <br />yielding. A Wilson analysis must show a well developed <br />destressed rib side zone, large pillar load carrying capacity and <br />a high factor of safety. The Wilson analysis using the design <br />parameters in Table 2 is summarized in Table 3. This analysis <br />provides the pillar response parameters required to satisfy the <br />observed pillar behavior. <br />Table 3 <br />Pillar Stability Analysis <br />1st North Mains <br />• <br />u <br /> <br />Parameter Calculated <br />Value <br />Width of rib side destressed zone (ft) 15.2 <br />Pillar load carrying capacity (ton) 13,900,000 <br />Factor of Safety 7.26 <br />2.3 Required Factor of Safety <br />A minimum factor of safety of 1.5 was used in previous permit <br />calculations. Experience at the mine site and calibration <br />calculations with the pillar design model used in this study <br />indicate that this is an appropriate value for the factor of <br />safety to ensure a stable mining geometry. As required by the <br />permit, the proposed mining geometry results in a factor of <br />safety of 2.0 or greater for overburden depths up to 600 ft. <br />2.4 Barrier Pillar Design <br />Barrier pillar design uses the same pillar <br />used in pillar design for secondary mining <br />However, the anticipated pillar loading is <br />the method outlined by Wilson (1977, 1981, <br />This method assumes that a portion of the <br />Cyprus Orchard Valley Mine <br />Panel C Pillar Analysis <br />design model as is <br />of floor coal. <br />modified according to <br />1982a, and 1982b). <br />overburden load <br />March 72, 1992 <br />page 4 <br />