Figure 14-18.—Using angle prism for sighting 90° from the
center-line stakes.
Cross-Section Leveling
In profile leveling, you determine the eleva-
tions of a series of points lengthwise along a
highway. In cross-section leveling, you determine
the elevations of points on a succession of lines
running at right angles to the lengthwise line of
the highway. The principal purpose of profile
leveling is to provide data from which the depth
of fill or cut required to bring the existing
surface up to, or down to, the grade elevation
required for the highway can be determined.
Note that profile leveling provides this data
relative to the center line. In figure 14-16, you can
see along the top the depth of cut or fill required
at each station to bring the existing surface to
grade—the prescribed grade line for the highway
is indicated by the smoothly curved grade line
shown. At each station, you can determine the
cut or fill by counting the squares between the
profile and the grade line.
The cross-section lines are established at
regular stations, at any plus stations, and at
intermediate breaks in the ground. Short cross-
lines are laid out by eye, but long crosslines are
laid out at a 90° angle to the center line with the
transit. For short crosslines, most surveyors prefer
to use an angle prism for sighting 900 angles from
the center line. Figure 14-18 shows a surveyor
using an angle prism for sighting a 900 angle from
the center line of the highway.
For cross-section leveling, strip topography,
and some other purposes, it is necessary to lay
off a 900 angle at numerous points along a line.
This 900 angle can often be established by
4-18
Figure 14-19.-Laying off a 900 angle from the center-line
stakes.
estimation with sufficient accuracy for the
particular job. The surveyor straddles the point
on the line, arms extended sideward along the
marked line (fig. 14- 19). By looking alternately
right then left, he adjusts the position of his feet
until his body is in line with AB. He then brings
his hands together in front of him, thus pointing
along an approximate 900 line from the marked
line. An experienced surveyor can lay off a 900
angle by this method so that a point 100 ft away
will be within 1 ft of the true perpendicular.
You should measure all elevations at abrupt
changes or breaks in the ground with a rod and
level. Measure all distances from the center line
with a metallic tape. In rough country, the hand
level can be used to advantage for obtaining cross
sections if the center-line elevations have been
determined by use of the engineer’s level.
Cross-section leveling is usually done with a
hand level after the profile run has been made.
The method is as follows:
From the profile run, you know the center-
line elevation at each station. Suppose you want
to take cross-section elevations at 10 ft intervals
for 40 ft on either side of the center line. The first
thing you do is to determine the vertical distance
from the ground to your line of sight through the
hand level when you stand erect with the level at
your eye. The best way to do this is to sight on
a level rod held plumb in front of you. Suppose
you find that the vertical distance is 5.5 ft. Then
your HI at any center-line station is the center-
line elevation (obtained in the profile level run)
plus 5.5 ft.
