Underground Utilities

For an underground utility, you will often need to determine both line and grade. For pressure lines, such as water lines, it is usually necessary to stake out only the line, since the only grade requirement is maintaining the prescribed depth of soil cover. However, staking elevations may be necessary for any pressure lines being installed in an area that (1) is to be graded downward or (2) is to have other, conflicting underground utilities.

Gravity flow lines, such as storm sewer lines, require staking for grade to be sure the pipe is installed at the design elevation and at the gradient, or slope, the design requires for gravity flow through the pipe.

Grade for an underground sewer pipe is given in terms of the elevation of the invert. The invert of the pipe is the elevation of the lowest part of the inner surface of the pipe. Figure 29 shows a common method of staking out an underground pipe.

Figure 30 shows another method of staking out an underground sewer pipe without the use of battens. Drive nails directly into the tops of the batter boards so that a string stretched tightly between them will define the pipe center line. Keep the string or cord taut by wrapping it around the nails and hanging a weight on each end. Similarly, the string, or cord, gives both line and grade.