It is important to choose poles that
are long enough and strong enough to adequately support the suspension cable
with the lateral pipe, water and Floppy Sprinklers, at a height that will allow
free movement of tractors, implements and harvesters underneath the system. Creosote poles can be used, with
the H5 specification recommended for anchor poles, and the H4 specification for
support poles.
The length of a pole is determined by a number of
factors, the most important being the height of the equipment used beneath the
overhead system. Say for example 4 meters high.
To this must be added:
* The depth that the pole is buried
in the ground
|
0.9 m |
| * The portion of the pole above the
securing height of the cable |
0.1 m |
* The length of the Floppy
Sprinkler, the saddle and the pipe
|
0.28 m
|
* The distance the cable, spanning
75m, is deflected when loaded
|
0.42 m |
* The clearance and a safety factor
that must be allowed
|
0.3 m |
| |
|
Sub-total
|
2.0 m |
| |
|
* The height of the equipment used
beneath overhead system
|
4.0 m |
| |
|
| Total length of pole |
6.0 m |
Care must be taken when digging or
drilling the holes for the poles, they must be accurately positioned and they
should not be very much bigger than the poles. Although nominally 0.9m deep,
the actual depths of the holes may be varied slightly, especially is there is a
pronounced dip in the ground. Some holes might then be a little shallower in
order to maintain the required clearance beneath the structure. Conversely
holes positioned on a small mound should not be dug any deeper as this will
adversely affect the clearance.
Before
planting poles in their appropriate holes in the ground, screw the M12#90 couch
screws and washers into pre-drilled 8mm holes, 100mm from the top of the poles.
Make sure that the screws in the anchor poles face towards the inside of the
field, and those in the support poles are at 90° to the direction of the cable
before starting to backfill.
Backfilling
of holes should be done in layers of not more than 150mm between compactions as
soil does not compact very well if the layers are much more than this. Soil
that is too wet does not compact well either, it should have a moisture content
of not more than 15%.
Poles
must be erected vertically and in straight lines. This can be achieved by using
a spirit-level, a mason’s line and sighting the work by eye.
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