I am new to the Northeast. All of my experience has in been in the state of Florida. I am currently working on a project in Vermont. I had set 3'x5/8" rebar driven down to ground elevation as my control. All level work was done with a digital level and all of my closures were less than .01'. After the first freeze I have found that my control is no longer talking. After some research, I found that "frost heave" might be the culprit. Since I don't know anyone in the area I thought I'd ask on here how common is this? How much movement should I expect? Also my points don't seem to be varying in horizontal values, only vertical. Is this common? I'm seeing vertical movement of up to 2" so far. I have luckily set some TBMs on solid concrete piers which I will use to re-establish new values on my control after the winter is over. Being new to the cold I was not anticipating this. Any tips, tricks, lessons learned would be greatly appreciated.
I'm not a surveyor, but having grown up in Buffalo I think I can speak with at least a little experience on this.
A 3' rebar isn't going to be long enough to get below the frost line. In Buffalo, I believe we planned for at least 5' to get below the frost line. I'm not sure how accurate this map is, but it seems to back up my experience...
Hope that helps,
Tim
My truck tells me the frost heaves are more than 2".
on very cold winters in the relatively mild clime of Maryland, we have seen frost heave on 18" and 12" rebars. as much as fifteen hundredths of a foot on one project
you have to remember that the original purpose of rebar's defomations is for bonding with concrete. so imagine the 18" rebar in the ground, vertically. frosty ground is going to grip the top of the bar by its deformations and there will be an upward force. i don't know how much, but it will be there.
as a counterpoint, that is why the expensive markers (from catalogs like Berntsen) use smooth rod, NOT rebar. having said that, i am an advocate of crosscuts on concrete curbs. this gives some advantage with both depth and mass, not to mention they are already in the ground
For local knowledge I suggest contacting the NGS State Advisor, Dan Martin. On the issue of frost heave on monuments in extreme environments, see: http://people.ucalgary.ca/~moorman/Engineering%20Geology.pdf
Brrrr!
DMM
Ditto all the others. A frost proof monument will be a smooth rod driven to refusal and thats inside (and not touching) an empty pvc or other cylinder thats been driven or inserted to below the frost line.
Otherwise, expect some heave in frost. How much will depend on the nature of the soil and its moisture content. You might no get any, or it could be sveral inches.
Thanks for the interesting reading,
Chr.
I know some do not like this method, but all I ever set for benchmarks is a 60d spike into a tree or utility pole. Because of the reasons you have discovered.
Scott ....
Maybe in Michigan ...up around Nome and Kotzebue (and outlying villages) I have seen power poles "jack" upwards of .5' and settle the same. Unfortunately, that's usually all I have to use for benches, although I occasionally find piling that has been driven hard into the permafrost (permafrost can be over 2,000' thick, so no "driving thru the frostline"!!) Only way to keep on top of it is to run your loops spring thru fall to watch your movements, beoch is whether the beginning TBM is good! The old brass BLM monuments usually handle it well, rebar is a joke. Trouble is, everybody in the village either ties their boat or their dog to them!
-JD-
From my experience in northern Minnesota, the freeze thaw cycle each year will indeed "pump" monuments. Rebar is bad because of the rough texture for the soil to grab, but any monument is susceptible.
Scott ....
JD
I have also seen haeve and settlement in utility poles especially within the first year after installation. Poles can also shift vertically as the power companies add extensions and more high voltage lines to the poles.
This can happen without any help from the weather
Thanks for all the info gents. I really just wanted to ensure I wasn't going crazy. Knowing it is common place up here, I can plan for it in the future.
I found almost all of the concrete monuments in a 1950s ear plat, that is still mostly undeveloped. Even one of the back line monuments were in and within 0.5' of where they were supposed to be. Plat was mostly in a sandy soil, except this one angle point was in a depression that looks like it holds water from time to time, and had some peat and muck in the bottom. Found that 4" square, 36" long concrete monument too, frost jacked completely out of the ground and fallen on its side. No earthly reason for someone to go through that tangle to get to that monument, let alone pull in out and flop it over next to where its position was. Had to be frost jacking, it does strange things.
In upstate NY, the real upstate the frost rarely gets down to a foot. Usually 6" tops before the snow covers the ground and insulates it. In the road it freezes much deeper, because its plowed. Water mains are constantly breaking from frost.
I doubt a 3' rod will move in many areas.
And I've been digging holes for 25 years in the hard chocolate.
Will look for some pictures but BLM decided drive rod was ok for mons in the Yukon Kusko Delta and so thousands of 9’ -12’ Al3 rods were driven and 31/4” cap installed. Now 20 years later it looks like sunflowers scattered across tundra. Caps are 5 -8 feet above ground. Definitely highest thing in tundra.
Wow... that would make it hard(er) to "shoot the dimple!"
B-)
Loyal
We joked about BLM starting an expensive aluminum mushroom farm.
i remember meeting a gent for ngs that was on a leveling crew in alaska. they were setting marks with sectioned rods and threaded ends, driven by a gas hammer. one marker seemed to never find refusal, keep adding sections, etc. a little while later, boom. the rod curled off a rock and back upwards into their own truck tire.
that photo reminds me of his story
Had that happen a few times while driving Al3 rod. You learn to always start checking the ground around you when you have driven 9 feet and it’s still going in good. After a while you learn what it feels like when it’s turned back up.
The gas hammers are called cobras but most take on a pet personal name because they are so finicky and they hurt your body to operate them.
