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American Tunnel bulkheads #2 & #3 Page 10 January 15, 2001 <br /> Appendix A. American Tunnel Bulkhead #2 design calculations (Continued) <br /> Hydraulic pressure gradient for 10-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#2, maximum pressure head <br /> _ HYw _ 640(62.4) Z77 <br /> P- 144 — 144 — psi <br /> Required bulkhead length with low pressure grouting on concrete/rock bulkhead contact: <br /> L= 4 = ai = 6.76ft <br /> Pressure gradient with L= 10 ft pg = i = 2107 = 27.7 psi/ft <br /> Factor of Safety against water leakage along concrete/rock contact around 10-ft thick <br /> bulkhead is: <br /> FS = 2717 = 1.41 <br /> American Tunnel Bulkhead #2 depth below surface (Z) required to prevent hydrofrac of rock <br /> around tunnel by 640-ft hydraulic head (277 psi pressure head): (Einarson& Abel, <br /> 1990) <br /> Bp= 3Q ,; —Q,,. =2Qo,e =2Z(144) =2Z(i44,, ,, )= 2.403Z psi=277 psi <br /> Z= 2.403 = 115 ft <br /> Therefore, the planned location for the American Tunnel Bulkhead #2, between Station <br /> 19+96 ft and Station 20+20 inside the American Tunnel portal with a minimum overburden <br /> of 762 ft will not be subject to formation hydrofracturing. <br /> Concrete shear on American Tunnel Bulkhead #2 perimeter: <br /> fg =2 f, =2 3000 = 110 psi (ACI 318-95, Sec 11.3.1.1) <br /> phf 277(13.5)14 52400 _ <br /> I'— 2(h-4% — 2(13.5+14)110 — 6050 — 8.66 ft <br /> W=phV=277(13.5)14(144) = 7,539,000 lb <br />