A manual of the principles and practice of road-making: comprising the location, construction, and improvement of roads, (common, macadam, paved, plank, etc.) and rail-roads. By W. M. Gillespie ...

SETTING GRADE PEGS. 145
SETTING GRADE PEGS.
The line of the road having been marked out by the
methods which have now been given, and stakes set at
the end of every chain, small " level pegs" are then to be
driven beside them, with their tops at the surface of the
ground, and their heights above or below the intended
height of the road (i. e. its " grade line") are to be ascertained by a levelling instrument, and the corresponding
"Cut" or " Fill" marked upon the large stakes.
Another form of the levelling field-book, better adaptec
for this work than that given on page 98, though less safe
for beginners, is presented below. It refers to the same
stations and levels, noted in the previous form of page 98,
and shown in fig. 43.
Ht. Inst. Total
Sta. Dist.. S. above F. S. Heighs.
Datum.
A 0.00
B 100 2.00 +2.00 6.00 -4.00
C 60 3.00 -1.00 4.00 -5.00
D 40 2.00 -3.00 1.00 -4.00
E 70 6.00 +2.00 1.00 +1.00
F 50 2.00 +3.00 6.00 -3.00
15.00 18.00 -3.00
In the above form it will be seen that a new column is
introduced, containing the Height of the Instrument, (i. e.
of its line of sight,) not above the ground where it stands,
but above the Datum, or starting-point, of the levels.
The former columns of "Ascent" and "Descent" are
omitted. The above notes are taken thus. The height
of the starting-point or "Datum," at A, is 0.00. The
Instrument being set up and levelled, the rod is held at A.
The Backsight upon it is 2.00; therefore the height of
the Instrument is also 2.00. The rod is next held at B.
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