Page 349 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

ROADWAYS 8.11

FIGURE 8.7 Slope stakes.

Since the cut and fill operations are directed toward reaching subgrade, much confusion will
be avoided by making all such stake markings refer to subgrade, using the symbol SG.
A misunderstanding as to whether figures on grade stakes are for grade or subgrade can be very
expensive.
Centerline stakes are quickly lost in most heavy grading, and the work is checked mostly by
slope stakes. However, as sections are brought near the correct subgrade, the center stakes are
replaced, and additional lines of markers are used to show the crown or cross slope of the road,
and shoulders and gutters.
Stakes at the edge of any grading area should be set back about 6 inches to 1 foot, so that they
can serve as a guide without interfering with the work.
It is frequently necessary to remove spilled dirt or level around a stake by hand, so that the
operator can read it and see whether the grade is high or low in reference to it.

Blue Tops. The final or fine grading operation is often guided by blue tops. These are usually 2 2
grade stakes driven down until tops are at subgrade. The tops are often colored with blue crayon to
make them more visible. Any that are driven below the surface are marked by a light stake alongside.
An expert grader operator can work over blue tops without disturbing them. However, it is
necessary for a person on the ground to remove spill piles that hide them, and to expose them if
they become buried. Even with this precaution, varying numbers of these stakes are caught by the
blade, or rolled over by tires, so that they have to be reset.
To set blue tops, a telescopic level of any type is set up, and its height (HI) figured from a
benchmark. The correct rod reading for grade is figured for each stake location from the center or
the theoretical grade profile, with allowance for crown or banking where necessary. The rod
worker starts the stake and holds the rod on top of it, and is told by the instrument operator how
high it is. The rod worker drives the stake the approximate distance, another reading is taken, and
the process is repeated until the top is within a few hundredths of feet of grade.
It is common practice to set blue tops 50 feet apart along the length of the roadway, and at 12-
to 15-foot spacing across it. The 50-foot spacing sometimes produces a low, wavelike effect, as a
grader operator may get the grade perfectly at the stakes but have a tendency to run consistently
high or low between them. This may be prevented by reducing spacing to 25 feet.