Here's a pic of a monument the crew found yesterday.
It's a little discussed topic, but we all know pavements (pc concrete and ac concrete) move a noticable amount with age, temperature, etc.
In a ten year period working highway construction I documented several x's and nails that 'moved' around seasonally.
Most of the time it was expansion and contraction in a predictable 'longitudinal' direction, however I do remember one "x" in a pc concrete intersection that was on an almost 4% grade, left to right.
When repeatedly observed over a period of time (a year or so) in a longitudinal line, it was evident that the pavement was 'sliding' downhill at about 0.04' per year. Don't know if it ever stopped..the job was finished.
Be careful when chasing 'hunnerts'..there may be things happening that aren't immediately evident.
:bored:
IMO: Pavement expands as a unit and contracts as individual panels, and will never contact up hill.
Some sidewalks in NYC, particularly in the outer boroughs were built using bluestone slabs from the upstate regions.
Trying to run lines up and down the streets in College Point used to give everyone headaches, as the slabs would move every which way over the years. It wasn't uncommon to find cross cuts off by an inch or more.
> Be careful when chasing 'hunnerts'..there may be things happening that aren't immediately evident.
Yes, but usually you have a clue whether the monuments are stable are not. There's the appearance of the vicinity, for one thing. If the mark is in a curb and the curb is jacked all out of what by thermal expansion, odds are good there's been movement. On the other hand, an old cast-in-place concrete curb inlet ought to be fairly stable horizontally.
In soil, if the monument is in clay soil on a hillside, the odds are excellent that it isn't stable. If the wooden utility poles and fence posts are leaning off plumb, the odds are even better.
Of course when you tie several monuments together with survey measurements all doubt vanishes. One of the great advantages to GPS is you can actually tie much of this stuff to a coordinate system delivered via the CORS network that is one helluva lot more stable than any monument that can easily be left in unstable ground.
Maybe it would be better to not place any monuments in unstable areas, remove the uncertainty, and only use the CORS coordinates. Avoid the problem.
Survey Dates could become important..... itrf velocities, and all! The land owners could want stakes, and the plat would have a TIME frame, that it could be used. I like it!
🙂
N
What if you live an a clay mountain side? Say your markers are moving down slope at 0.04 feet per year. OK they are all moving and so is your improvements. So after a hundred years or so is the house you built on a zero setback moved onto the adjacent lot?
> What if you live an a clay mountain side? Say your markers are moving down slope at 0.04 feet per year.
What that usually means is that in three or four years your boundary markers will be so out of plumb that they will look obviously disturbed. After enough time, they will be laid over nearly horizontal. The mechanism by which objects founded in the top layer of clay soils shift doesn't usually apply to structures, so just the boundary markers will move.
Actually on a slope in areas that freeze I think all soils will move downhill above frost depth. I've found stones that were about horizontal. Longer pipes stand up better but will lay over pretty good. Not having the CORS from a hundred years ago I usually just give it my best estimate from where I believe the base is (or was) and straighten it up from there.