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American Tunnel bu.Lkheads #2 & #3 Page 3 January 15, 2001 <br /> magnitude earthquake along the Ridgeway Fault, 25 miles to the <br /> north (Sullivan, et al, 1980; Weisser, 1982; Knight Piesold Co. , <br /> 1988) . The deep beam bulkhead design specifies 11-foot thick, #10 <br /> rebar on 6-inch centers at the downstream (portal side) form face, <br /> #6 temperature and shrinkage rebar on 12-in centers on the <br /> upstream (mine side) form face, 3. 5-inch minimum concrete cover <br /> between the #10 rebar and the form faces, Type 5 sulfate resistant <br /> cement and 3, 000 psi concrete meets all design requirements, as <br /> shown in the Appendix B calculation sheets. Pipe cut-outs in the <br /> downstream rebar cage will require 5-foot long, 450 angled, #10 <br /> corner trim bars to eliminate any possibility of concrete corner <br /> cracking when the bulkhead is fully loaded. <br /> After the walls are scaled, the rock wall surfaces should be <br /> either parallel to the tunnel axis or tapered. Irregularities <br /> along the scaled rock wall must project into the concrete in order <br /> to fully mobilize the design concrete shear strength. <br /> Approximately 8 .3% (6, 640 in2) of the 79, 200 in of the Bulkhead #2 <br /> perimeter tunnel perimeter along the 10-foot long bulkhead is <br /> required as latite irregularities projecting at least 0. 16 inches <br /> into the tunnel to assure that the design concrete shear strength <br /> is achieved at the 277 psi design pressure head. Approximately <br /> 8 . 8% (7, 550 in2) of the 85, 540 in of the Bulkhead #3 perimeter <br /> tunnel perimeter along the 11-foot long bulkhead is required as <br /> latite irregularities projecting at least 0. 14 inches into the <br /> tunnel to assure that the design concrete shear strength is <br /> achieved at the 335 psi design pressure head. <br /> A milk of lime buffering pile is recommended between the <br /> coffer dam and the upstream form face of Bulkhead #2 because of <br /> the acidity of the water entering the American Tunnel at the <br /> fractured rock zone between Station 27+00 and Station 31+00. <br /> Sincerely, <br /> -0-4 7 . a,W, <br /> John F. Abel, Jr. <br /> Colorado P.E. 5642 <br />