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Memo to Russ Means 6 November 14, 2007 <br />Bulkhead Cost Estimate' file No. M-2007-044 <br />Design for Concrete Shear on Pack Rat Mine 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 />I _ pxhxF. _ 116x9xI2 2.7 feet <br />2x(h+t')x f'S 2x(9+12)x110 <br />where: L = bulkhead length (feet) <br />p = pressure head (psi) <br />h = adit height (feet) <br />? = 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 Continaencv .Bulkhead .for Construction Cost Estimating Purposes <br />The basic design elements for the Pack Rat Mine 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 10' x 2.8' long <br />• bulkhead volume is 13.5 cubic yards <br />• low 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 3/4 inch aggregate, Type V cement, 1.6 percent fly ash, pozzolan, <br />water/cement ratio of 0.45 by weight, and will be over sanded to enhance pumpability <br />Bulkhead Construction Cost Estimate <br />DRMS has estimated the cost to install the three bulkheads described above at $531,247.00. This <br />estimated. cost includes all indirect costs and. the five percent administration cost required by statute. The <br />estimated costs are detailed in the worksheet memo enclosed. The esti.rnate uses adjusted unit costs <br />incurred during the construction. of the Terry Tut riel bulkhead. in. the Sunnyside Mine during the mid-1.990s. <br />A copy of the detai.l.ed. `berry 't'unnel bulkhead costs is also enclosed with this menio. <br />Verification of Bulkhead Effectiveness <br />For water impounding bulkheads in underground mines to be effective, there must be no significant <br />hydrogeologic flow path between the impounded 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 monitoring plan to be required for the Whirlwind Mine (see DBMS memo: bate <br />Pickford to Russ Means, 11-&-0 7) must focus on establishment of a baseline that will be useful in <br />demonstration of eventual bulkhead effectiveness. In addition., and as discussed above, in the Whirlwind <br />Mine setting where there are multiple aquit"ers in a relatively flat lying sedimentary stra€igraphy,