Page 81 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

SURVEYS AND MEASUREMENTS 2.31

Each work crew that needs grade checks has a
stadia rod, and a target with rechargeable battery
that can be clamped to it, similar to that shown in
Fig. 2.28.
It is of course very important that the laser beam
elevation be accurate. The instrument is set up in
somewhat the same manner as a self-leveling engi-
neers’ level, by adjustment of three leveling screws.
It is turned on, and allowed a 2-minute warmup
period before being placed in automatic rotation.
This rotation may shut off automatically if the
instrument is disturbed.
A rod and target are set on a benchmark, and a
reading is taken. If the elevation is a fractional num-
ber, it can be rounded off for greater convenience by
lifting or lowering the laser slightly, using a fine
vertical adjustment on top of the motor head.
The laser may have a distance range adjustment,
which should be correct for job conditions. It may
cover an area from 600- to 2000 foot in diameter.

Oscillation. When work areas are typically long
and narrow, as in trenching or highway jobs, the
laser head may oscillate from side to side, in an arc
of 30° or more, instead of rotating.
This oscillation may be quite rapid, and is used
more often in automatic control of depth of excava-
tion than as a reference for work crews.

Grade Laser Beacon. The Grade Laser Beacon
manufactured by Laser Alignment Inc. is useful in a
variety of ways on agricultural and construction jobs.
The model shown in Fig. 2.29 is being used for site
grading. Seen in that figure are uses with a target on
a surveyor’s rod and a receiver mounted on a grading
FIGURE 2.28 Target on surveyor’s rod.
machine. The beacon is portable and self-leveling, (Courtesy of AGL Lasers.)
and indicates when elevation changes have occurred
by a disturbance. It is waterproof, can be set for two
separate alignment sights, and is workable for an area of 2,000-foot diameter. In addition to site
preparation work, it is useful for agricultural land leveling, construction slope control, and ditch
excavation.
The laser beam rotation control can be adjusted to 6, 12, 20, or 40 revolutions per second for
optimum performance. It would be set at lower rps to save battery life, but the higher speed is
needed for use with fast-moving equipment using the laser beam received by hydraulic sensors to
adjust for cutting grade. This use with equipment will be explained shortly. The manual adjust-
ments by the equipment operator may be done with a slower laser rps. But the faster the beam rota-
tion, the quicker the grading equipment response, preventing a washboard effect on the graded
surface.
For slope control the Grade Laser Beacon is directed up perhaps a 2:1 or 3:1 slope to guide the
grading machine or surveyor’s rod holder. The slope grade can be set at a range from 4 to 50
percent. This instrument can be set with two grades set simultaneously on the illuminated grade
display. That is useful when two pipelines coming together have different slopes, for example, the
feeder lines and the main pipeline. In another case the side slopes for a ditch will probably be
steeper than the bottom area running to the water trickle channel.