HOW TO SET SLOPES (FALLS/GRADES)
7
Working Example (Continued)
Important note: All “grade facility” rotary lasers revert back to the auto (self) level condition if
switched O without retaining the gradient set. So its recommended to complete the ground-
works before switching the laser O.
Once this 1:40 fall is set, the User can use this inclined laser beam as a datum to set the depth of
either the crown of the drainage pipe or the Invert level, anywhere in range of the laser – along
that same axis.
Invert level of a pipe – is the level taken from the bottom of the inside of the pipe.
Crown of a pipe – is the Invert level plus the internal diameter of the pipe plus the pipe wall
thickness. It may be necessary to use this in calculations when level measurements are taken
from the crown of a pipe.
Manhole / Access Chambers:
A manhole or access chamber is required to gain access to a drainage system for un-blocking,
cleaning, rodding or inspection. (Land drainage systems excluded). They can be manufactured in
PVC, masonry or pre-cast concrete.
When setting appropriate drainage gradients it is important to allow for the depth down to
either the crown of the pipe (or the Invert level) from ground level, when using these manholes.
Dual Grading:
A rotary laser level with dual grading facility can be used for setting out driveways, car-parks or
areas with slopes (falls) in BOTH the X & Y axis.
The same procedure is adopted as above for drainage runs, except a second step in the process
is undertaken to set the laser to a fall in the other axis, to complete the dual grade setting-out.
Cut & Fill Machine control work:
If slopes of more than 10% (1:10) are required, which is outside the range of electronic
adjustment of the rotary laser’s prism; then simply switch the laser to Manual & t a “Laser
Grade Adapter” between the top face of the tripod & the base of the laser. Then set the required
slope. Search our website for more details.
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