I went out an measured a state highway roadway surface on a tiny 2-foot+- grid for 28 feet of width and 150 feet of length. It was a TON of shots. Knowing I needed redundancy I went back and re-measured the exact same surface at a different time of the day. There is no uniform error. It doesn't affect the outcome of the survey, but it is worrisome to see a mismatch. The 0.01'contour map showed all the same slopes, and looked almost exactly like the original, but I found that the heavier traveled lane of the roadway had actually changed elevation by a couple hundredths, not completely uniformly. I initially blamed it on my instrument, but in the base line parallel to the travel lanes the elevations all matched within 0.01 feet. Have any of you seen roadway elevations go up and down depending on traffic? Some of it is 18-wheelers. These were short foresights, and my vertical index was calibrated before each trip. I found my unit off by 15 seconds before the first trip, and I calibrated it, and also again before second, and checked it with multiple reverse and direct shots and got superior accuracy. Really has me stumped. I just went out in office parking lot and shot points and checked with level, and the elevations are right. Hmmmm... any suggestions? Have you seen well established roadways do this over a one week span?
> I went out an measured a state highway roadway surface on a tiny 2-foot+- grid for 28 feet of width and 150 feet of length. It was a TON of shots. Knowing I needed redundancy I went back and re-measured the exact same surface at a different time of the day. There is no uniform error. It doesn't affect the outcome of the survey, but it is worrisome to see a mismatch. The 0.01'contour map showed all the same slopes, and looked almost exactly like the original, but I found that the heavier traveled lane of the roadway had actually changed elevation by a couple hundredths, not completely uniformly. I initially blamed it on my instrument, but in the base line parallel to the travel lanes the elevations all matched within 0.01 feet. Have any of you seen roadway elevations go up and down depending on traffic? Some of it is 18-wheelers. These were short foresights, and my vertical index was calibrated before each trip. I found my unit off by 15 seconds before the first trip, and I calibrated it, and also again before second, and checked it with multiple reverse and direct shots and got superior accuracy. Really has me stumped. I just went out in office parking lot and shot points and checked with level, and the elevations are right. Hmmmm... any suggestions? Have you seen well established roadways do this over a one week span?
in LA, hot weather, soft pavement, and heavy trucks? yes, deflection should be expected, especially on asphalt. concrete should not show as much.
what kind of prism are you using? some of the 360's can have a +-0.03 ft error per measurement, vertically
Yes. And much more.
Simple physics depending on the base and the weight of traffic.
I have taken multiple shots on tarmac before, nearly after and after that all varied by several hundredths.
Stuff moves. That is part of how it keeps from breaking up at times.
Do not set up on asphalt, it is unstable, was one of the first things I was taught. I have found that to be good advice. Asphalt is always moving, sometimes slow and sometimes quickly.
jud
rutting and deformation will be a function of the grade of oil, mix design/ fracture of the agregate, tempurature, loading, resistance of the subgrade mat'l, and speed.
that's why they are called flexible pavements-
Asphalt Is Properly Called Flexible Pavement.
I can recall when I worked at Bethlehem Steel doing roadway maintenance and watching 2" waves in the asphalt roads as Euclid 35s (off road quarry dumps) hauled a full load of hot slag at top speed.
Paul in PA
Asphalt Is Properly Called Flexible Pavement.
Asphalt is actually correctly called Bitumen
Around here our roads are paved with something called Asphalt Concrete or AC for short.
The asphalt is only the binder for the aggregate.
It's kind of like calling Portland Cement Concrete (PCC) cement.
Very common mistake.
JRL
I have monitored HEAVY foundations that move. Everything in the world moves. It is simply a matter of where, why, when, how and how much.
It seems you have identified where and how much.
What are you using for a topo foot on your prism pole?
The wheel ruts tend to have more asphalt oil on top as the rock gets pushed down. Between the ruts will have more rock on top and be more stable. If you are just using a typical prism point, the tip may be sinking into the asphalt more as the road heats up. The problem will be worse if the top layer is sealcoat as compared to hotmix.
Just a thought.
James
rounded tip to prevent this. I tested heck out of it and can find no more than 0.005 foot differential between shots during each survey as caused by this. Shot a shot on top of pebble, then down beside one the best I could force it. Did it many times. Thanks for the input though.
Frank
I suspect that the instrument "compensator" is two close to vibrating road traffic or there is a compensator issue with your instrument.
Your sights will be have to be under 150 m to generate +-1.0 mm results early in the
day to avoid air heat distortions.
I run test elevations single site over 100 m from instrument robot and record elevation on test point. Then run auto collimation routine with the geo 650 and see at worst +- 1.0-2.0 mm week to week apart on same procedure to test point.
You did not specify the Fault lines or the contract did not specify for example
""
Please pick up at 60 cm grid with attention to fault lines to generate a +-2.0 mm
random shot to any point on submittal Tin surface as surveyed by date ""
If you placed your GPS base next to work site and forced your rover to agree with
your precise robot levels through site just scrap the robot and use gps
the spec is land mine to cause grief maybe until robot is fixed.
Asphalt does move
Please list the equipment you used and the contract submittals
There has seem to be a lot of compensator issues lately on the board regard
trimble S6 series maybe chase that. best of luck the site seems small so i say the
prism or instrument & compensator are out or to close to run routine correctly??
To check you compensator sight farpoint and tip instrument with foot screw farpoint elevation should change little
A so called Certified shop in Seattle installed wrong or wrong part compensator on my instrument
and the instrument would not correct for tilt.
The instrument had to go to the Good shop to be fixed in Colorado
Peter K
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