Page 93 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

SURVEYS AND MEASUREMENTS 2.43

distance, the same for each stake, above grade. They are usually spaced 50 feet apart for uncom-
plicated work, and 25 feet for superelevations, vertical curves, and other special situations.
Reference grade is level with the centerline on straightaways. On superelevated (banked)
curves, the reference is to the tipped plane of the cross section, so that it will be lower than the
near edge on the inside of a curve, and higher than it on the outside (Fig. 2.38).
A tack is driven into the top of each hub for precise location of horizontal alignment.
Setting Up. A string stake is driven alongside each hub, about 1 foot to the outside. It must be
vertical, and driven deep enough for good stability. The rod should extend directly toward the
stake, and can be slid inward or outward until its slotted end is directly over the tack. The brack-
1
et is raised or lowered until the rod is ⁄ 4 inch above the selected stringline height. Adjustments are
locked with setscrews.
A steel engineers’ rule is used to measure the height of the rod, and to check its location over
the tack.
Take-up reels are then placed, 25 feet before the first stake in the section, and 25 feet past the
last stake. These should be offset 12 to 18 inches beyond the end of the line of the string, with the
crank to the outside. The reel is first located on the ground, stakes are driven through holes in its
base, and it is then raised to a convenient cranking height, and clamped.
A metal midpoint stake is driven in line with the string stakes, halfway between the last (or the
first) one and the reel. The rod may be at stringline grade, or higher.
The string itself is reeled off a storage reel (or two reels if there are two lines) held on a bar on
a truck. It is anchored by winding about 25 feet onto one of the take-up reels, and is paid out as
the truck drives to a few feet beyond the other end. The string is cut and secured to that reel.
The string is pulled taut by hand and by turning the reels. Then it is inserted into each rod
notch. It should slip into them easily, but require moderate force to be pulled out. Slot openings
can be widened with a screwdriver, or narrowed with pliers. There should be no visible sag
between stakes.
Using an engineers’ rule, adjust the rod brackets so that the string is at its exact height above
the tacks, and with a plumb bob to make sure it is in line. Sight down the completed line, and
recheck any break in a smooth flow.
Visual inspection should be repeated just before use, and occasionally as work progresses.
Any breaks in the string can be repaired by relaxing the tension, tying the broken ends togeth-
er with a square knot, and retightening.

MEASURES OF PRODUCTION

IN-PLACE MEASUREMENTS

Distance. Surface distances may be measured approximately by pacing, stadia, or car
speedometer; or more exactly by tape (chaining), the distance meters mentioned earlier, or mea-
suring wheel.
Distances may also be read off job plans or maps. But a possibility of an error in a map, or in
interpreting it or its scale, must be guarded against.
A measuring wheel is a convenient and sufficiently accurate means for measuring both short
and long distances. Small wheels are hand-rolled along the ground, while large ones may be either
hand-rolled or towed slowly by a vehicle. A counter registers the distance covered in feet.
Readings down to 2 inches may be obtained. See Fig. 2.40.

Bank. A bank of earth or other material may be measured before and during the time it is dug
away. This is usually done to establish a basis for payment to the owner of the land, or from the
job to which it is being hauled.