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5 November 14, 2007 <br />Merna to .buss Means 1{ile No. M-2007-044 <br />Bulkhead Cost Estimate <br />With their close proxirn.ity, the second decline bulkhead can be constructed using the same design as the <br />main bulkhead, with the exception that a bypass pipe will not be needed, and a pressure monitoring tube <br />will be required. The criteria .for the contingency of a :Pack Rat iViine bulkhead is determined as follows. <br />Hy,t, _ 268 x 62.4 =116 psi <br />p 344in~ l ft2 144 <br />where: fI =hydrostatic head (feet) <br />~,, =water density (62.4 pounds per square foot) <br />p =pressure head (psi) <br />Potential for Hydrofracin~ at the Proposed Secondary Bulkhead <br />72xBp <br />H= <br />Y <br />where: H =height of overburden in feet <br />Bp =breakdown pressure <br />~=rock density in pounds per cubic foot <br />For the proposed secondary bulkhead the required minimum overburden height to prevent hyrofracing is 80 <br />feet for the 3.04 pcf overburden rock densisty and the 13 6 psi maximum hydraulic pressure, as follows: <br />72x316 <br />H . 104 = 80 feet <br />This design. criterion is exceeded for essentially any selected bulkhead location in the Pack Rat Mine. <br />17esiun far Hydraulic Pressure Gradient Secondary Bulkhead <br />~ 1.6~si , 2~.2 i?~t <br />L;fn.grouted Bu3k:noari l; ~= _5__- .~~..ff_..~t ::- J ~. ; <br />p~ ,r <br />3 '1 Eipsi,,,,. _ 2.8 'eet <br />:flow Pressure Grouted Bulk3.~ead 1. - ~l"psi J~~t - ~ <br />Clearly, with an eight fold decrease in required bulkhead length, and the Jiff culty in concrete pouring .for <br />bulkheads greater than 10 feet in length, low pressure grouting is a necessity for the Pack Rat Mine <br />contingency bulkhead. <br />