1 - Alaska Energy Data Inventory

C. Hydraul ic Losses in Machine Bored Tunnel (IVIBT). Since a contractormay elect to construct an MBT, a detailed analysis of hydraulic losses wasperformed. These calculations appear in Hydraulic Appendix B2, figure ~."Minor" losses were calculated in the normal manner using various HOC andincluded; transitions to and from shotcrete sections, surge tank tee,horizontal and vertical bends, gate structure transitions, trashracks,entrance, rock traps and gate slots. Based on a discussion with arepresentative of the Robbins Company and ~istrict geologists, an expectedoverbreak of 1/2 inch was arrived at. Maximum and minimum overbreak wasthen judged to be 3/4 inch and 1/4 inch respectively. The overbreak valueswere used as the effective roughness (K s)' which resulted in relativeroughness (11.0 ft/Ks) of 528, 264 and .176 for the mi n imum, expected andmaximum loss conditions. By using the Von Karman-Prandtl equation (HOCchart 224-1) the following friction factors were arrived at:ConditionMinimum LossesExpected LossesMaximum Lossesoarcy-Weisbach IIfll0.02250.0280.032Manning "n"0.01640.01830.0196o. Refilling of Tunnel Turnouts. It is expected that the contractorwill widen sections of the tunnel for his own convenience. There wassome concern about the hydraulic losses that these turnouts would cause,and therefore some thought was given to the possibility of the contractorrefilling the excess tunnel cross-sectional area with shotcrete.Calculations. showed that with a discharge of 400 ft 3 /s, the combinedcontraction and expansion losses amounted to 0.068 ft (a 15 degreetransition was assumed). Further investigation showed that because ofreduced velocities, the lower friction loss through the increased flowarea available in the turnout would more than make up for the contractionand expansion losses. Friction losses through the turnout were 0.0407 ftwhile friction losses through the same length (175 ft) of unlined tunnelwith a 12.2 ft diameter is equal to 0.187 ft. The combined loss for thecontraction - expansion (0.068 ft) plus friction losses through theturnout (0.0407 ft) totaled 0.109 ft while the friction loss through theBl-22