Laserfiche WebLink
Memo to Tom Schreiner 4 February 21, 2006 <br />Bulkhead Cost Estimate Permit No. M-1983-141 <br />pressure gradient of 41 psi/ft. Using these criteria allows the following calculations of bulkhead length for <br />the pressure gradient component of the design: <br />Ungrouted Bulkhead <br />I,ow Pressure Grouted Bulkhead <br />L _ 265 psi = 53 feet <br />Spsi/ ft <br />L _ 265 psi = 6.5 feet <br />41 psi / ft <br />Clearly, with an almost ten fold decrease in required bulkhead length, low pressure grouting is a necessity <br />for the proposed main bulkhead. <br />Design for Concrete Shear on Mount Royale Adit No. 1 Perimeter, 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's = 2 f'~ = 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 sheaz strength than the <br />concrete, so concrete sheaz 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_ pxhxQ _ 265x8x8 =4.8feet <br />2x(h+C~x f'g 2x(8+8x110 <br />where: L =bulkhead length (feet) <br />p =pressure head (psi) <br />h = adit height (feet) <br />B = adit width (feet) <br />f', =concrete shear strength (psi) <br />Therefore, the 6.5 foot minimum bulkhead length required for pressure gradient exceeds the bulkhead <br />length requires for concrete sheaz, and pressure gradient controls the design at this stage of the analysis. <br />