Laserfiche WebLink
• strata, with a uniaxial compressive strength of approximately <br />10,000 psi, and a tensile strength of approximately 700 psi. In <br />the unlikely event of a failure in the main roof beam (unit R2), to <br />the shale parting (unit R3), the massive sandstone upper roof beam <br />(unit R4), will be able to stabilize the span across the main <br />entries. <br />The maximum possible height for any roof cave is therefore expected <br />to be approximately 11 ft. above the coal seam. There is no <br />likelihood for any roof span failure in the main entries to <br />propogate to surface. <br />(b) Pillar Stability <br />The main entry pillar configuration is illustrated in Figure A, <br />which forms pillars that are 80 ft. long and 60 ft. wide. The <br />maximum expected height of the pillars for a conservative stability <br />analysis is 10 feet. <br />• <br />Confined Core Pillar Strength <br />The pillar strength calculations have been adapted from the method <br />presented by A.H. Wilson in Ref. 4, and utilize results from coal <br />strength testing undertaken during the exploration program. <br />Determined from laboratory test data: <br />So = Uniaxial Compressive Strength = 4650 psi <br />~ = Angle of Internal Friction = 36.6° <br />y = Average material density = 150 pcf <br />Calculated: <br />tan S = Passive Pressure Coefficient <br />= l+sin ~ <br />1-sink S <br />C = cohesion = <br />2,~ tan 8 = 1169 = 1170 psi <br />• Ex. 7-2 <br />