Figure 15-54.Turning point and level notes.

Figure 15-52.Computing cut-or-fill requirement from a missing grade stake.

Equipment Operator Basic - Beginning construction equipment operators manual
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nearby, but you do have a nearby grade stake at station 4 + 00 and a set of the project drawings. At station 4 + 00, the project drawings call for a subgrade elevation of 240.0 feet. The stake at station 4 + 00 calls for a fill of 7.0 feet; therefore, the existing elevation at station 4 + 00 is 233.0 (7.0 feet below 240.0). You set up your level and take a backsight direct reading on station 4 + 00 of 4.0 feet. The backsight reading of 4.0 feet plus the existing known elevation of 233.0 feet gives an instrument height of 237.0. Then you take a foresight shot on station 4 + 50 and get a direct reading of 4.5 feet. You subtract the foresight reading of 4.5 feet from the instrument height of 237.0 feet, and you get at station 4 + 50, the existing elevation of 232.5 feet. The project drawings show that the finished sub- grade elevation at station 4 + 50 is 239.0 feet. With the existing elevation at 232.5, you must FILL at station 4 + 50 a total of 6.5 feet to reach the 239.0 feet required subgrade elevation. Therefore, you should place a grade stake at station 4 + 50 that is marked F 6.5. TURNING POINT.— The two missing grade stake examples were based on elevations of nearby points that could be read from one setup of the level. If differences of elevation or distance are too great or if there are obstructions, you will have to make an inter- mediate setup and sight on a point, called a turning point (T.P.). Any convenient point may be used as a turning point, but the level rod must be set on firm ground or on some firm object so that the elevation of the T.P. will not change while the rodman waits for the levelman to setup at the new position. An example of a level run is shown in figure 15-54. You have a B.M. at the bottom of a bank and you want to find the elevation at the top of the bank, which is point A. You cannot set up on the top of the bank to take a reading on the level rod held on point A because to take a backsight shot on the B.M., the level rod is too short. First, record the B.M. elevation of 120.0 feet. Next, set up the level instrument on the bank and take a backsight shot on the B.M. to get a level rod reading of 10.2 feet. Add the backsight shot of 10.2 feet to the B.M. elevation of 120.0 feet to get the first instrument height of 130.2 feet. Then take a foresight shot on the T.P. to get a level rod reading of 1.2 feet. Subtract the 1.2 feet foresight reading from the 130.2 feet instrument height to get a T. P. elevation of 129.0 feet. Next, move the instrument to the top of the bank. Take a backsight shot on the T.P. to get a level rod reading of 9.8 feet. Add the 9.8 feet backsight reading to the 129.0 feet T.P. elevation to get a second instru- ment height of 138.8 feet. The last step is to take a foresight shot on point A to get a level rod reading of 3.8 feet. Subtract the 3.8 feet foresight reading from the 138.8 feet second instrument height to get a 135.0 feet point A elevation. Some level runs may require more than one T. P.; however, no matter how extensive the job, the proce- dure is always the same: you add and subtract succes- sive rod readings from a point of known elevation to the point of unknown elevation. MEASURING HORIZONTAL DISTANCES Setting or replacing grade stakes requires measur- ing horizontal distances with either a woven tape or a steel tape. Figure 15-54.—Turning point and level notes. 15-32

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