1 - Alaska Energy Data Inventory

conditions. After going through a series of calculations to find themaximum and minimum losses as shown in the following paragraphs theexpected "n" value was rounded off to 0.031.b Maximum and Minimum Losses - With the expected value of "n" =0.0315, a Oarcy-Weisbach friction factor of 0.0186 was calculated by theequation:f = 185 n 2(Dm) 1/3(Ref 21, p. 6-15)where:f= Oarcy-Weisbach friction factorOm= Circular equivalent of horseshoe tunnel; in this case, 11.4 ft.n= Manning's "n"HOC chart 224-1/6 was then used to find the relative roughness (15.2 onthe x-axis) corresponding to a friction factor of 0.0186. The effectiveoverbreak, including effects of scalloping along with normal tunnelroughness was equal to 0.75 ft (11.4 ft/15.2 ft). To obtain maximum andminimum "f" values, "auxillary" curves parallel to the fully rough curvewere drawn on HOC chart 224-1/6 (see figure 7-38 in Appendix 82). These"auxillary curves represent approximate limits of maximum and minimum losscoefficients for the tunnels that were being consiaered. A vertical linewas drawn through the fully rough line at the expected relative roughnessof 15.2. The intersection of this vertical line with the two auxillarycurves resulted in maximum and minimum "f's" of 0.099 and 0.069respectively. Which were then converted to equivalent Manning's "n" of0.029 and 0.0347.c Sensitivity to Tunnel Size - It is the general experience intunnel construction that the average as-built tunnel diameter is largerthan the design or nominal diameter and this project will be no exception.If the completed tunnel has an average diameter of 12.2 ft with an81-16