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  #21  
Old 02-27-2014, 01:35 PM
bobw bobw is online now
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Jim - thanks for the PMs...helpful as always

Kiril - How accurate do you think the "cheap" solution can get? For us, we'll have 40 or 50 sleeves on a site, so 80-100 spots to dig. Some investment in time in the burying is worth it given how our guys lose so much time in the finding. But... if we can have reasonable accuracy, and use GPS to get us to the right area and maybe combine with rebar laid out to allow us to do an exact hit...we may be getting somewhere quite useful. How far down can the metal detectors people are using pick up rebar? Our sleeve ends are usually 36" down for road crossings... of course they go in so early that you have to assume +- or 12"
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  #22  
Old 02-27-2014, 02:12 PM
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1idejim 1idejim is online now
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Quote:
Originally Posted by bobw View Post
Jim - thanks for the PMs...helpful as always

Kiril - How accurate do you think the "cheap" solution can get? For us, we'll have 40 or 50 sleeves on a site, so 80-100 spots to dig. Some investment in time in the burying is worth it given how our guys lose so much time in the finding. But... if we can have reasonable accuracy, and use GPS to get us to the right area and maybe combine with rebar laid out to allow us to do an exact hit...we may be getting somewhere quite useful. How far down can the metal detectors people are using pick up rebar? Our sleeve ends are usually 36" down for road crossings... of course they go in so early that you have to assume +- or 12"
This might answer your metal locator questions
http://www.trenchlessutility.com/PDF...d%201d2100.pdf
These are different than metal detectors.

The EMS markers may be your best bet in locating the sleeves.

http://www.rhinomarkers.com/DP_Produ...p?id=3M_BURIED

If I were in your situation and wanted quick, accurate location I would combine a basic entry level gps (to put me in the general area) and EMS to pinpoint the sleeve.
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  #23  
Old 02-27-2014, 03:26 PM
SoCalLandscapeMgmt SoCalLandscapeMgmt is online now
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You can always try these..... pretty inexpensive too.

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  #24  
Old 02-27-2014, 03:29 PM
SoCalLandscapeMgmt SoCalLandscapeMgmt is online now
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In all seriousness though.... I would think that the EMS route would work the best. It would be the most accurate and the quickest. It would just be a matter of investing in the markers. I bought a used Dynatel locator on E-Bay a few years back for like half the cost of new and it works pretty damn well for locating wire paths and that sort of thing.
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  #25  
Old 02-27-2014, 03:34 PM
SoCalLandscapeMgmt SoCalLandscapeMgmt is online now
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Juniper Systems also makes some interesting hand held GPS based mapping solutions for the construction industry but the accuracy of the GPS is only listed at 2 to 5 meters. Probably wouldn't be accurate enough for your needs but I thought I'd throw it out there since a lot of you are tool and equipment nerds like I am.

http://www.junipersys.com/
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  #26  
Old 02-27-2014, 06:52 PM
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1idejim 1idejim is online now
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You can always try these..... pretty inexpensive too.

Ah-ha. The infamous mumble mumble locator. I can't have nuthin nice.
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  #27  
Old 02-27-2014, 08:29 PM
Kiril Kiril is offline
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Originally Posted by bobw View Post
Kiril - How accurate do you think the "cheap" solution can get? For us, we'll have 40 or 50 sleeves on a site, so 80-100 spots to dig. Some investment in time in the burying is worth it given how our guys lose so much time in the finding. But... if we can have reasonable accuracy, and use GPS to get us to the right area and maybe combine with rebar laid out to allow us to do an exact hit...we may be getting somewhere quite useful. How far down can the metal detectors people are using pick up rebar? Our sleeve ends are usually 36" down for road crossings... of course they go in so early that you have to assume +- or 12"
It depends on the unit you get and your surroundings. Biggest problem in urban environments is multipath rejection, which wreaks havoc on both accuracy and repeatability. High end survey grade units with a RTK base station can mostly overcome this depending on where you locate the base station.

That said, I have used some high end consumer grade units (not mapping grade) with DGPS reported accuracy at 4 feet. You might look into some 3 meter mapping grade units that have an optional external antenna that is better at picking up signals in urban environments (i.e. to deal specifically with multipath rejection). That will still be considerably cheaper than a survey grade unit with a base station. You also might look into some precision ag units/antennas.
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  #28  
Old 02-27-2014, 08:40 PM
Kiril Kiril is offline
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Just looked at ebay. There are some used GeoXT's for under $2,000. Those are sub-meter units.
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  #29  
Old 03-03-2014, 09:34 PM
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pls8xx pls8xx is offline
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At the sleeve ends this what I like to do ....



I use polyester rope for the bright color. Hold it vertical as you backfill and cut the rope flush with the surface. When you come back a scratch of the surface uncovers the rope. Follow it down to the sleeve end. The knot tells you when to slow up digging.

For those of you that want to go the GPS route, I recommend you try two identical cheap units. Find something to use as a base marker that is just out of the project limits that will survive construction. With one unit at the base marker and the other unit at the sleeve end, make a simultaneous coordinate reading of both units. Record the difference in both the Northing and Easting.

When you come back to look for the sleeve, put one unit at the base location. Take the other unit where you think the sleeve might be. Once again make simultaneous readings. Add the recorded difference of Northing and Easting from the original to get the current correct coordinates for where the sleeve is. Compare that coordinate to the current reading and it will tell you how far to go north and south, east and west. Make a new simultaneous reading to confirm that you now have the same amount of difference in coordinates as you did when you laid the sleeve.

Do I need to make a graphic?
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  #30  
Old 03-03-2014, 09:38 PM
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Why knot
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