Leveling the tape

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Slope Chaining

Basic Engineering

Laying off a given distance

LEVELING THE TAPE. Figure 12-13 shows a pair of chainmen making a horizontal measurement on a slope. You can see that, to make the tape level, the person at the lower level is holding the end at chest level while the person at the higher level is holding it at knee level. To maintain the tape in a horizontal position, the chainman at the lower level held the hand level. By studying the position of the other chainman, he decided that it would be possible to hold the tape at chest level. He then held the hand level at about the height of his own chest level and trained it on the other chainman. It indicated that a level line from his own chest level intersected the person of the other chainman at that persons knee level. So he called out, "At

Figure 12-13.-Horiziontal chaining using plumb bobs.

your knee!" thus informing the other chainman where to hold the end of the tape.

BREAKING TAPE. The term

Generally, you will start breaking tape when the slope of the existing ground exceeds 5 percent (this depends also on the height of the chainmen). The reason for breaking tape is that the chainman on the lower ground will have difficulty in holding the tape steady and horizontal when his point of support exceeds his height. You also break tape to avoid hazardous measurements, such as crossing power lines and making measurements across a heavily traveled highway.

Now, to measure the distance AB shown in figure 12-14, the chainmen may proceed as follows: The rear chainman stations himself at point A. The head chainman pulls the tape forward a full tape length uphill toward point B and drops it approximately on line with the two range poles. He then comes back along the tape until he reaches a point at which a partial tape length, held level, is below the armpits of the rear chainman at point A. At this point, the head chainman selects a convenient whole-foot graduation, and the chainmen measure off the partial tape length (distance Aa) from starting point. As shown in the figure, the head chainman must be holding at the 60-ft mark to measure Aa. Then, he calls out, "Holding sixty!" so that the rear chainman knows what graduation he is holding when the measurement is made. As in other chaining methods, the rear chainman always checks the alignment.

After the pin is placed, the rear chainman (leaving the tape lying in position) moves forward to point a and gives a pin to the head chainman who, in turn, moves to point b; to make sure that the rear chainman takes the right graduation, he calls out, "Hold Sixty!" This procedure is repeated until a full station is measured or until a full-tape length measurement can be resumed. You see that to measure distance bc, both chainmen will probably use plumb bobs to transfer the distance to the ground.

Remember that the rear chainman gives the head chainman a pin only at each INTER-MEDIATE point of a tape length. He keeps the pin at full tape lengths to keep track of the number of stations laid out as in ordinary horizontal chaining.