I normally use mag nails to set my RTK base on. These are not left on site and are only there for the duration of the project then we pull them when we finish.
We have a project coming up where our base will be set on the same location for about 3 weeks. I was looking for ideas on something a little more sturdy and that might have a better indentation in it to position the fixed height tripod on.
Depending on the soil type the mag nails are not that sturdy and with us setting up on this one 20+ times I was looking for something better.
I thought about maybe some large rebar (3/4"?) that I could pound in the ground a a foot or two and then drilling a hole in the top of it to position on?
Curious what ideas others might use. Again this does not need to be permanent just something solid for 3 weeks of daily use.
We use these and we use a drill as you describe to mark a precise point. Works well for us.
We used 5/8" rebar 24" long with a red cap that says control point.
For a control point, you can do a lot of things, get a fence post digger, dig a 2 foot hole fill it with concrete drive a mag nail before it sets.
Sometimes just a paint spot works.
We use 24" rebar with aluminum caps that are center punched.
http://www.berntsen.com/Surveying/Survey-Markers/Aluminum-Survey-Markers
Drive a wood hub flush. Then set a mag nail in the top.
When I need a permanent traverse point similar to what you describe, I set a 1/2" rebar with a plastic cap marked traverse point. It works very well for my part of the world.
Take the timber spikes (like from Lowes or Home Depot) and put them in a vise and either drill a dimple or simply use a center punch. The flared top of the head will keep it in the vise without shooting it to the floor.
You can't do exactly the same thing for rebar. Find a size and length suitable for your needs and drive it down flush and make a punch mark into it. I assume that these will be set in areas that they wouldn't be confused for a property monument. If they won't be confused, I don't see the need for a fancy cap on it.
Carl
Years ago we started driving 60d nails thru a beer cap to make them more stable.
I now use 2in roofing spinners and large washers because pull tabs on beer cans don't work well.
Most of the GPS control points I set for long term use are 1/2in rebar with plastic cap driven 6in below surface grade.
B-)
But now you don't have an excuse to drink beer!
I forgot to add that beer cans are smashed and put atop hubs and corner monuments set in roads and under sod to let one know you are close to your point while digging.
B-)
Or you could go really "old school" and set an empty whisky bottle.
Of course they don't work too well with magnetic locators, and you have to be careful with the spade when recovering them. But glass lasts for thousands of years in the ground don't you know 🙂
Unless you are in a real rocky area, dig a post hole 2 feet deep and take a 48" X 5/8" Rebar and drive in the center, then back fill the hole with concrete and center punch the rebar. You could also embed an eye bolt into the concrete to secure your base to. To keep it from being confused for a boundary monument, document it on your plat as a control point.
I have recovered those from 25+ years ago and they are still solid but the heads degrade and you will have trouble finding the drilled hole. They also work very well for probing and digging a little. Get the galvanized as the others rust and become nasty.
We mainly work in an arid region without alkali soils... In most areas. Thy hold up very well here.
We always buy the galvanized ones. Plus, they really make a schonstedt sing!
> Curious what ideas others might use....
A rebar with plastic cap is ubiquitous. I'd prefer 1/2" or larger, but some use 3/8". Some go as short as 12" partly to avoid hitting underground utilities, partly a cost issue. I'd say 18" minimum, 24" better. You want more than half of it below the frost line.
When I worked in British Columbia in the early 1990's nobody there knew what a plastic cap was. Property corners there are marked with 1/2" square galvanized bars with the letter "BCLS" stamped in the side. In '93 I worked in Whatcom County, WA for a year and was introduced to the rebar and plastic cap. When I returned to Canada in '94 I showed off a plastic control cap I had in my vest pocket and the boss about went nuts. The local equipment supplier took a while to figure out where to get them. I pointed out the various ads in the magazines (this was a time before the internet). Anyway, that small shop BCLS in Chilliwack may have been the first guy in the province and maybe the country to use plastic caps on his control points and may still be the only one for all I know.
Our conditions are 48" annual rainfall, fog often, salt spray, acidic soils.
I had a patio installed and the contractor used non-galvanized landscape spikes. I used the few that were leftover and I was given rusty hands.
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