CONCRETE PIPE & BOX CULVERT INSTALLATION - American ...

INSTALLATION
LINE AND GRADE
For sewer and culvert construction, line and
grade are usually established by one or a combination
of the following methods:
• reference line established by a helium-neon
laser
• control points consisting of stakes, spikes,
plugs or shiners set at the ground surface and
offset a certain distance from the proposed
sewer centerline
• control points established at the trench bottom
after the trench is excavated.
• trench bottom and pipe invert elevations while
excavation and pipe installation progresses
Specially designed helium-neon lasers are available
for sewer and culvert construction. Basically
the instrument converts input power into a beam of
light, which is projected as a narrow beam rather
than shining in all directions as does a light bulb.
The light beam is a continuous, uninterrupted string
line, which does not sag and can be used for distances
up to 1,000 ft. (90 to 150 m). The laser projects
a beam of light the diameter of which depends
on the distance being projected and on the optics
of the particular instrument. Usually the beam is
about the size of a pencil. Since the laser beam
is a light beam, it is seen by either looking back at
the instrument or intercepting the beam with target,
which reflects the light.
As with any surveying instrument, the initial setting
is most important. But once a laser is set as
to direction and grade, it provides a constant reference
line from which measurements can be taken
at any point along the beam. A workman with any
12
American Concrete Pipe Association • www.concrete-pipe.org