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Memo to Russ Means 4 November 14, 2007 <br />Bulkhead Cost Estimate File No. M-2007-044 <br />Cleazly, with an eight fold decrease in required bulkhead length, low pressure grouting is a necessity for the <br />proposed main bulkhead. <br />Design for Concrete Shear on Main Bulkhead <br />The length of the bulkhead must be sufficient to keep the sheaz stress developed in the bulkhead concrete <br />below the ACI 318-891imits. Sheaz strength of concrete is related to its compressive strength as follows: <br />f', = 2 f'~ = 2 3000 =110psi (ACI 318-89, Section 11.3.1.1) <br />where: f', =concrete sheaz strength (psi) <br />f'~ =concrete compressive strength (psi) <br />It can be assumed that the adit wall rock at the bulkhead location has higher shear strength than the <br />concrete, so concrete sheaz will control the design. The required bulkhead length for the concrete sheaz <br />component of design, assuming minimum bulkhead concrete compressive strength is specified at 3000 psi, <br />is calculated as follows: <br />L_ pxhxe _ 64x9x12 =1.Sfeet <br />2x~h+2~x f', 2x9+12x110 <br />where: L =bulkhead length (feet) <br />p =pressure head (psi) <br />h =decline height (feet) <br />k =decline width (feet) <br />f', =concrete shear strength (psi) <br />Therefore, the 1.6 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 />Desigrt of the Main Bulkhead for Construction Cost Estimating Purposes <br />The basic design elements for the proposed main bulkhead aze 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 1.6' long <br />• bulkhead volume is 7.7 cubic yards <br />• low pressure grouting is necessary <br />• flexural and temperature shrinkage rebaz at both ends of the bulkhead, both ways <br />• stainless steel bypass piping is necessary <br />• Concrete will use maximum'/, inch aggregate, Type V cement, 16 percent fly ash, pozzolan, <br />water/cement ratio of 0.45 by weight, and will be over sanded to enhance pumpability <br />