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JOWN F. ABEL, JR. <br />MINING ENGINEER <br />Mr. Steve Fearn <br />Silver Wing Co. <br />P.O. Box 299 <br />Silverton, CO 81433 <br />310 LOOKOUT VIEW COURT <br />GOLDEN, CO 80401 <br />803-279-4901 <br />FAX 27&8163 <br />JFA6el2®Comnnd.nst <br />July 23, 2003 <br />Reference: Bulkhead design, Mogul Mine ,..odifications <br />Dear Steve: <br />The following two modifications to the drawings for the <br />Mogul Mine, No. 1 Level bulkhead are approvE=d and recommended. <br />The 3-in diameter schedule 40 pipe braces for the forms can <br />be safely replaced with 2-in diameter schedule 40 pipe braces. <br />Design load for the assumed maximum 10-ft long 3-in diameter <br />schedule 40 pipe brace, fixed with respect 1.o rotation and <br />translation, is approximately 37 .kips, for <s 32.0 kip component <br />perpendicular to the bulkhead face. The shorter maximum 5-ft <br />length of the rotation and translation fixec9 2-in diameter <br />schedule 40 pipe braces have a strength of approximately 34 kips, <br />for a 29.9 kip component perpendicular to t]Ze bulkhead face. The <br />calculated fluid concrete form load on the i=wo upper level <br />central pipe braces is 5.35 kips and on the two lower level <br />central pipe braces is 6.09 kips. The factors of safety, 5.5 and <br />4.9 respectively, are acceptable and are deisigned to permit the <br />concrete within the bulkhead to be pressurized at the end of form <br />filling. <br />The 850 psi design strength No. 1 structural grade Douglas <br />Fir lagging can be safely reduced from 3 by 12-in to 2 by 12-in. <br />The load carrying capacity of the three 2-ft 6-in long simply <br />supported lagging boards placed in the access opening at the top <br />of the air side bulkhead form is 665 lb/ftz for the 2 by 12-in <br />lagging and 1847 lb/ftz for the 3 by 12-in lagging. The fluid <br />concrete load on the lower access opening board will be 375 <br />lb/ft2, 225 lb/ftZ for the central access opening board and 75 <br />lb/ft2 for the upper board. The design load carrying capacity of <br />continuous 2 by 12-in lagging is 998 lb/ft2. The maximum fluid <br />concrete load is 975 lb/ft2 applied to the lowest unrestrained <br />continuous lagging board, 6.5-ft below the back. The design load <br />