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Ransom Tunnel Bulkhead Page 4 May 7, 1997 <br /> Hydraulic pressure gradient: <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 /> Ransom tunnel bulkhead, maximum pressure head <br /> _ HY. _ 635(62.4) = 275 psi <br /> p— 144 — 144 <br /> Required bulkhead length for with low pressure grouting on concrete/rock bulkhead contact: <br /> L= 41 = aL7 = 6.7ft <br /> Pressure gradient with L= 8 ft pg = s = 28 <br /> 5 = 34.4 psi/ft <br /> Factor of Safety against water leakage along concrete/rock contact around 8-ft thick <br /> bulkhead is: <br /> FS = 3414 = 1.19 <br /> Ransom Tunnel bulkhead, depth below surface required to prevent hydrofrac of rock around tunnel <br /> by 635-ft hydraulic head (275 psi pressure head): (Einarson& Abel, 1990) <br /> Bp= 3Q,,,;,,—Umax =2uo,,b =2H(la4) =2H(7)= 2.403Hpsi = 275psi <br /> H= 2.403 = 114 ft <br /> Therefore, the bulkhead must be centered at least 320 ft inside the portal to develop 114 ft of <br /> overburden. Recommended bulkhead location from 319 ft to 327 ft inside the portal, for <br /> average distance from the portal of 323 ft and an average depth of 116 ft. <br /> Concrete shear on Ransom tunnel perimeter: <br /> fs =2 f, =2 3000 = 110 psi (ACI 318-95, Sec 11.3.1.1) <br /> phi2750010 27500 <br /> I'— [2(►i+]%] — [2(10+10)110] — 4400 — 6.25 ft <br /> W=phl = 275(10)10(144) =3,960,000 lb <br /> W 3960000 <br /> V` — [2(")1L.(144) — [200+10)]R(144) — 85.9 psi <br /> FS = = 85.9 = 1.28 <br /> 4 <br />