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Bulkhead Design for AMD Paae 16 October 27-29, 1998 <br />tl = 2° (26) <br />P = maximum allowable hydraulic pressure (psi) <br />S = design fiber stress (psi) <br />2 for two pipe walls <br />ti = required minimum wall thickness (in) <br />t2 = manufactured wall thickness (in) <br />D = nominal inside pipe diameter (in) <br />Cz = corrosion rate (in/yr) <br />The minimum estimated pipe life (Y) in years is: <br />Y - c~c,t (27) <br />The predicted life of the piping is conservative because the <br />concentration of corroding chemicals should decrease over time. <br />The piping should also contain waterstops to positively <br />prevent the acid mine water from moving along the outer surface of <br />the bypass pipe. The waterstops can be provided by thrust rings to <br />eliminate any reliance on skin friction to prevent the bypass pipe <br />from being ejected from the bulkhead. Figure 4 indicates the <br />combination of thrust rings and waterstops installed in the <br />American Tunnel Bulkhead. The individual stainless steel thrust <br />rings on the 12-inch inside diameter bypass pipe was designed to <br />resist the total thrust of 76,000 lbs from the maximum possible <br />head. <br />Earthquake Resistant Design <br />Acid mine drainage bulkheads should be checked for loading <br />resulting from the maximum credible earthquake. The American <br />Concrete Institute provides (ACI 318-95, Sections 9.2.2, 9.2.3, <br />9.2.5) the basis for evaluating earthquake loading. The total <br />design load is defined by different load factors, as follows: <br />U = 1.OSF + 1.40E (28) <br />U = design load <br />F = fluid load <br />E = earthquake load <br />The fluid load is the maximum water head acting on the <br />bulkhead. The earthquake load is defined by the acceleration of <br />the water impounded along the line-of-sight behind the bulkhead <br />plus the bulkhead itself. Figure 5 provides the Ransom Tunnel <br />plan, showing the anticipated 360-foot line-of-sight water <br />impounded upstream from the bulkhead. The calculations the Ransom <br />Tunnel Bulkhead earthquake loading factor of safety are presented <br />in Appendix A. <br />- 16 - <br />