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American Tunnel bu.Lkheads #2 & #3 Page io January 15, 2001 <br /> Appendix B. American Tunnel Bulkhead #3 design calculations (Continued) <br /> Hydraulic pressure gradient for trial 11-ft thick bulkhead: <br /> Low pressure grouting of concrete-rock contact but not rock, gradient allowable= 41 psi/ft <br /> (Garrett & Campbell-Pitt, 1958, Chekan, 1985, pl 1), with factor of safety of 4 <br /> American Tunnel Bulkhead#3, maximum pressure head <br /> Hyw 773(62.4) 335 <br /> P= 144 — 144 = PSl <br /> Required bulkhead length with low pressure grouting on concrete/rock bulkhead contact: <br /> L= a1 = 33' = 8.17ft <br /> 41 <br /> Pressure gradient with L= 11 ft pg = i = 311 = 30.5 psi/ft <br /> Factor of Safety against water leakage along concrete/rock contact around 11-ft thick <br /> bulkhead is: <br /> FS = 3015 = 1.34 <br /> American Tunnel Bulkhead #3 depth below surface (Z) required to prevent hydrofrac of rock <br /> around tunnel by 773-ft hydraulic head (335 psi pressure head): (Einarson& Abel, <br /> 1990) <br /> B,= 3Qin—a. =2Qo,,b =2Z(144) =2Z(i44)=2.403Z psi=335 psi <br /> Z = 2' = 139 ft <br /> Therefore, the planned location for the American Tunnel Bulkhead #3, between Station 3+67 <br /> ft and Station 3+82 inside the American Tunnel portal with a minimum overburden of 160 ft <br /> will not be subject to formation hydrofracturing. <br /> Concrete shear on American Tunnel Bulkhead #3 perimeter: <br /> fs = 2 f� =2,13 000 = 110 psi (ACI 318-95, Sec 11.3.1.1) <br /> pht _ 335(15)12 60300 = <br /> I'— 2(h4.0% — 2(12+15)110 — 5940 10.2 ft <br /> W=phQ = 335(15)12(144) = 8,683,000 lb <br />