I've set out a series of parallel irrigation lines 12.9 metres apart and about 570 metres long. I set star bars (steel star fence droppers)at the ends of each line and in the middle.
Sprinklers are spaced every 9 metres along the lines.
The challenge for those setting up the irrigation system is to get each sprinkler exactly on line.
The owners have imposed tight tolerances.
They used a laser set on its side which produced good results while the weather was kind but when it heated up and the afternoon sun bore down that method got a bit erratic.
I'm wondering what others have used in such circumstances?
It was suggested to stretch piano wire taught but its a fair way to stretch a wire (280 metres) and involves a fair amount of setting up.
This has been an interesting excercise as I was initially asked to set all the cross lines up but when they did the first line and came back next morning the pipe had shrunk aout 180mm over the 280m length. They then reverted to a length of pipe for a measuring stick (as opposed to 'fixed, non expandable' measuremnt with total station)that worked well in all temperatures.
Its an intensive vegetable cropping setup using gps controlled tractors.
The area is a vast estuary area with nice loam laced with beach shingle from 50 - 200mm diameter. Trenching has been a pain due to them and they have used tons of sand to bed it in. All up about 8km pipework.
What was the laser that went "erratic"? A good rotary shouldn't have an issue with 280 meters, they are used all of the time in the heat of the day.
Around here we would use common fence wire (barbed wire) stretched tight between two points on line or at a specific offset to facilitate final placement. 280 meters would be no problem as it comes in 1320-foot lengths. Wire stretchers would keep it tight no matter the temperature. A bar or two might be set along the line and the wire loosely attached to it to eliminate questions about lateral motion.
Why not simply set up on line and shoot in all the desired points?
What would be wrong with just double offsetting every other sprinkler, at say 5 ft on each side (or meters). That would give them the centerline every 18 meters. Should be no problem keeping that straight. Then forget about stringing some kind of line for 500 m, which I could see getting all messed up.
Another way could be to set up a perimeter grid, kind of like colume lines in a big building. Then they just intersect the grid lines and don't really have to measure much of anything.
Sounds like an interesting project.
Locate your end points and place a rig at each end to anchor a wire to that is on centerline of the run, get the wire straight and on the ground, use a marker cart, the kind that are used for football field markings and mark the line over the wire with lime. Remove the wire, dig the trench, assemble about a 100 feet or so of pipe using the pipe as the measuring tool and bed most of it leaving an end up to continue with the next sections, replace the wire for line and set each section in place under the wire using a plumb bob or long level, bedding it as you go. Repeat for each line, if your starting point for each additional line is perpendicular to the end of the first pipe, everything should be where it belongs when done. If you set the end points the contractors should be capable of the rest, if not, get someone else to do the work.
jud
Richard-
How about night time with optical theodolites at both ends of your control lines simultaneously to eliminate visual shimmering ?
Cheers
Derek
PS-
Do you not have any trained straight eyed Sarcophilus Harrisii ?
thanks for replies
Yes agree - wire seems to be preferred method.
They mark the trenches out with their GPS tractor and dig a 450mm bucket trench and just keep digging.
There just isn't room to set any intermediate points as there is literally gear, machines etc anywhere that isn't taken up with trench and spoil from the trench.
Thanks for comments on the laser as I have no use of one and so no knowledge either. I was dubious of them in such circumstances but obvioulsy no worries for a good one.
I don't know what sort of laser it is. They needed as second so they hired a Trimble branded one but but that would not flip on side so they got another which was all over the place at anytime of the day.
I checked their line setout with their current laser and it was good.
Its not best time of the year hear with most places shut down so not easy to get gear.
I'm just the gopher hired in to set it out, and its been a steep learning curve for them. I said I'd ask about and see what others thought on setting it all up. Some on site suggested a wire too.
Sarcophilus Harrisii
Derek thats a good one , but we hardly have any Sarcophilus Harrisii these days - they really are on the endangered list.
I'd sugegsted a theodolite but that means extra training and I don't think they would want that.
I'll try and write up a small post with some pictures when its all over.
Sarcophilus Harrisii
There must be some of those roaming around the Old South where locals keep proclaiming the sighting of the legendary chupracubra.