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Table 2. Pillar design calculation results. <br /> 25'x100' 25'x25' 50'x50' Units <br /> Density of Rock 162.79 162.79 162.79 lbs/cft <br /> Depth of Cover 250 250 250 ft <br /> Pillar Area 2,250 625 2,500 sgft <br /> Room Size 50'xl30' 104'x104' 208'x208' ft <br /> Pillar Support Area 9,750 10,816 43,264 sqft <br /> Pillar Stress 1,225 4,891 4,891 psi <br /> Rock Strength (measured) 19,580 19,580 19,580 psi <br /> Safety Factor 16.0 4.0 4.0 N/A <br /> Pillar Stress Calculation <br /> The average pillar stress(csp)in regular layouts of pillars can be estimated by assuming the <br /> overburden weight is equally distributed among all the pillars,known as the tributary area <br /> method: <br /> rr = x h x(Ct X Cz) <br /> P (WXI) <br /> (1) <br /> where 7' = specific weight of the overlying rocks <br /> h - the depth of cover <br /> It, - the pillar width <br /> 1 = the pillar length <br /> CI - the heading distance <br /> C2 - the crosscut center distance <br /> Figure 11. Equation used to determine pillar stress. Equation print from Esterhuizen et al., 2011. <br /> NIOSH recommends that the ratio of the stress caused by the weight of the rock above the pillar <br /> to the ability of the pillar to support the weight should be at least 4.0. This assumption is <br /> conservative since a safety factor of 1.0 would technically hold the rock mass. The NIOSH <br /> recommendation is typically utilized in underground blasted rock quarries. The blast induced <br /> damage to the pillar drives the recommendation of>4.0 safety factor. The Rose Red Quarry's <br /> Rose Red Quarry Geotechnical Report 17 ,,,,�,,.„,,.�„�,,,,,,,,, ,,,,,,,,,, <br />