nearby, but you do have a nearby grade stake at station4 + 00 and a set of the project drawings.At station 4 + 00, the project drawings call for asubgrade elevation of 240.0 feet. The stake at station 4+ 00 calls for a fill of 7.0 feet; therefore, the existingelevation at station 4 + 00 is 233.0 (7.0 feet below240.0).You set up your level and take a backsight directreading on station 4 + 00 of 4.0 feet. The backsightreading of 4.0 feet plus the existing known elevation of233.0 feet gives an instrument height of 237.0. Then youtake a foresight shot on station 4 + 50 and get a directreading of 4.5 feet. You subtract the foresight readingof 4.5 feet from the instrument height of 237.0 feet, andyou get at station 4 + 50, the existing elevation of 232.5feet.The project drawings show that the finished sub-grade elevation at station 4 + 50 is 239.0 feet. With theexisting elevation at 232.5, you must FILL at station4 + 50 a total of 6.5 feet to reach the 239.0 feet requiredsubgrade elevation. Therefore, you should place a gradestake at station 4 + 50 that is marked F 6.5.TURNING POINT.— The two missing gradestake examples were based on elevations of nearbypoints that could be read from one setup of the level. Ifdifferences of elevation or distance are too great or ifthere are obstructions, you will have to make an inter-mediate setup and sight on a point, called a turningpoint (T.P.). Any convenient point may be used as aturning point, but the level rod must be set on firmground or on some firm object so that the elevation ofthe T.P. will not change while the rodman waits for thelevelman 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 wantto find the elevation at the top of the bank, which is pointA. You cannot set up on the top of the bank to take areading on the level rod held on point A because to takea 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 abacksight shot on the B.M. to get a level rod reading of10.2 feet. Add the backsight shot of 10.2 feet to the B.M.elevation of 120.0 feet to get the first instrument heightof 130.2 feet. Then take a foresight shot on the T.P. toget a level rod reading of 1.2 feet. Subtract the 1.2 feetforesight reading from the 130.2 feet instrument heightto 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 rodreading of 9.8 feet. Add the 9.8 feet backsight readingto the 129.0 feet T.P. elevation to get a second instru-ment height of 138.8 feet. The last step is to take aforesight shot on point A to get a level rod reading of3.8 feet. Subtract the 3.8 feet foresight reading from the138.8 feet second instrument height to get a 135.0 feetpoint 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 thepoint of unknown elevation.MEASURING HORIZONTAL DISTANCESSetting or replacing grade stakes requires measur-ing horizontal distances with either a woven tape or asteel tape.Figure 15-54.—Turning point and level notes.15-32

Integrated Publishing, Inc.

6230 Stone Rd, Unit QPort Richey, FL34668

Phone For Parts Inquiries: (727) 493-0744
Google +