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6 November 14, 2007 <br />Memo to Russ i~teans File No. M-2007-044 <br />.Bulkhead Cost Estimate <br />Desi n for Concrete Shear on Pack Rat Kline Perimeter <br />The required bulkhead length .for the concrete shear component of design, assuming minimum bulkhead <br />concrete compressive strength is specified at 3000 psi, is calculated as follows: <br />_ pxhx~ _ 116x9x12 =2.7feet <br />L 2x(h+E}x f'S W 2x(9+12}x110 <br />where: L =bulkhead length (feet) <br />p =pressure head (psi) <br />h = adit h.ei.ght (feet) <br />Q = adit width (feet) <br />f'S =concrete shear strength (psi) <br />Therefore, the 2.8 foot minimum bulkhead length required for pressure gradient slightly exceeds the <br />bulkhead length required for concrete shear, and pressure gradient controls the design. <br />Design of the Pack Rat Mine Contin~enc~Bulkhead for Construction Cost Estimating Pu~oses <br />The basic design elements For the Pack Rat M.tne bulkhead are as follows. <br />Note: one foot added to Whirlwind Mine workings dimensions to account for notching of bulkheads <br />• bulkhead dimensions are 13' x i0' x 2.$' long <br />• bulkhead volume is 13.5 cubic yards <br />• iow pressure grouting is necessary <br />• flexural and temperature shrinkage rebar at both ends of the bulkhead, both ways <br />stainless steel bypass and monitoring piping is necessary <br />• Concrete will use maximum 3/a inch aggregate, Type V cement, 1.6 percent fly ash, pozzolan, <br />waterJcement ratio of 0.45 by weight, and will be over sanded to enhance pumpability <br />Bulkhead Construction Cost Estimate <br />DBMS has estimated the cost to install the three bulkheads described above at S53I,247.00. This <br />estimated. cost includes alI indirect costs and. the five percent administration cost required by statute. The <br />esti:rnated costs are detailed in the worksheet ruemo enclosed. 'Che estirnate uses acl,~ustecl unit costs <br />incurred cluri:ng the crsnstY:uction ofthe "I~err~° '1'u~~r~el bulkhead in the Sunr~.yside Mine c~luring tho rt~id-1.990s• <br />,~ copy ot'the detailed. Terry Tunnel bulkhead costs is also enclosed ~,vith this rnen~o. <br />"4'eri.lication ofBulkhead. Effectiv€;ness <br />For water impounding bulkheads i.n underground mines to be effective, there must be na signi.fican.t <br />hydrogeologic flow path between the irnpoun.ded mine pool and surface water bodies. Demonstration of <br />this is done through establishment of baseline surface hydrology conditions and monitoring for <br />perturbations to baseline following bulkhead installation. Ground water tracers can be a useful tool. The <br />ongoing hydrologic tnorFitoring plan to be required for the; Whirlwind Mine (see DR'v1S rr~emo: Kate <br />i'ickford to I7uss Means, 11-$~07) must focus on estal?l.ishment of a baseline that ~vil.l be useful. i.~1 <br />demonstration. of eventual bulkhead etfectiveness. In addition., and as discussed above, in the Whirlwind <br />Mine:. setting where there are multiple aquifers i:~ a .relatively flat lying sedirr~entary stratigraphy, <br />