station where you will set a hub. Consider fig-ure 10-19, for example. This is a plan showing a linerunning from a curb inlet through two manholes to anoutfall. The dotted lines are offsets (greatlyexaggerated for clearness) to points where you will setthe hubs. Note that at stations 5 + 75 and 1 + 70.21,you set two hubs, one for the invert in and the otherfor the invert out.The invert elevations at the manhole (MH) aregiven on the profile. Suppose that the invert out at CI“A” #2 is 122.87 feet. The gradient for this pipe is 2.18percent. Station 8 + 50 lies 0.50 station from CI “A”#2; therefore, the invert elevation at station 8 + 50 is122.87 feet minus (0.50 x 2.18), or 122.87 feet minus1.09, or 121.78 feet. You compute the invertelevations at the other intermediate stations in thesame manner.Suppose now that you are starting the stakeout atCI “A” #2. The final-location party left a center-linestake at this station. You occupy this point, turn 90degrees left from the line to MH “A” #1, and measureoff the offset; for example, 8 feet. This is presumingthat, if the ground slopes across the line, the high sideis the side on which the hubs are placed in figure10-19. Hubs are always placed on the high side toprevent them from being covered by earth dozed offto form a bench for the trench-digging rig.You drive a hub 8 feet offset from station 9 + 00and determine the elevation of the top of the hub. Thevertical distance from the top of the hub to the invertat station 9 + 00 is the difference between the invertelevation and the elevation of the top of the hub. Theinvert elevation at station 9 + 00 is 122.87 feet.Suppose the elevation of the top of the hub is 126.94feet. Then you would mark the guard stake for thishub, CI “A” #2 inv. C 4.07´. Suppose the elevation ofthe top of the hub driven at station 8 + 50 is 127.33.The invert elevation at this station is 121.78; therefore,you would mark the guard stake for this station, 8 +50, C 5.55´.The manner in which the construction crew willuse these hubs to dig the trench to grade will varyaccording to the preference of the supervisor for oneof several methods. One method involves the erectionof a batter board across the trench at each hub. The topof each board is placed on the posts at a set distanceabove invert elevation; for example, 10 feet. Fig-ure 10-20 illustrates this method.Take station 9 + 00 in figure 10-19, for example.The elevation of the top of the hub is 126.94 feet andthe invert elevation is 122.87 feet. To be 10 feet aboveinvert elevation, the top of the batter board must beplaced on the post 5.93 feet above the top of the hub.To get this distance, the field constructor would simplyFigure 10-19.—Sewer stakeout plan.10-20