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Strength of Orchard Valley Mine "D" Seam Coal: <br />Various physical compression tests and in situ tests have been performed on <br />• coal at the Orchard Valley Mine. <br />From available data, only one set of compression tests (1984) and one set of <br />in situ tests (1979) have provided the physical property data needed for <br />pillar stability calculations using A.H. Wilson's method of pillar design. <br />Test results and graphical analysis are included in the Appendix. The <br />recommended pillar design values are used from the in situ tests done in 1st <br />East. The recommended values are ~ (anyle of internal friction) = 33.4°, <br />Tan B = 3.45, and oo (rock (coal) mass cohesion) = 217 psi. These values <br />are more conservative than the physical compression results obtained from 8 <br />North and 9th East. <br />Variations of the physical property strengths at the Orchard Valley Mine <br />have been laryely attributed to the predominate face and butt cleat and the <br />anyle at which these intersect the mining direction. <br />By using the most convervative data, the pillar design will be conservative <br />• and if deviations occur, the safety factor would increase. <br />• <br />