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Memo to Russ Means 4 November 14, 2007 <br />Bulkhead Cost Estimate File No. lV1-2007-044 <br />Clearly, 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 shear stress developed in the bulkhead concrete <br />below the ACI 318-89 limits. Shear strength of concrete is related to its compressive strength as follows: <br />f'S = 2 f'r = 2 3000 =110psi (ACI 318-89, Section 11.3.1.1.) <br />where: f', =concrete shear 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 shear will control the design. The required bulkhead length for the concrete shear <br />component of design, assuming minimum bulkhead concrete compressive strength is specified at 3000 psi., <br />is calculated as follows: <br />L= p x h x , _ 64x9xl2 =1.5feet <br />2x(h+G)x f'S 2x(9+12)x110 <br />where: L = bulkhead length (feet) <br />p = pressure head (psi) <br />h = decline height (feet) <br />f = 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 />L si n.qf the.. a4n Bulkhead for Construction Co,stlstimatin <br />The basis: design elements for the proposed train. bulkhead are as follows: <br />Note: one foot added to Whirlwind lil.i.ne 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 rebar at both. ends of the bulkhead, both ways <br />stainless steel bypass piping is necessary <br />Concrete will use maximum '% inch aggregate, Type 4' cement, 16 percent llt? ash., pozzolan., <br />water/cement ratio of 0.45 by weight, and. will be over sanded to enhance pumpability