Hub & Tack curb staking

How is he going to know if your tolerence is something less that 1/4"?

Exactly!

I still think SMIƒ??s Construction 5 program was the best at staking out roadways. You could stakeout a station/ offset and it would give you 2 options. Come or go with a left or right of line or a perpendicular distance to the centerline. Make curb stakeout a breeze.

Amen! So many things about SMI that I wish the current programs incorporated. The ability to access so many functions with just a few keystrokes.

Everyone knows the hub & tack has a 1/8" tolerance.

In the middle of this one now ?ÿits a double crossover diamond under I-24 in Paducah. Interstate icrosses over to the right of this sheet and then there is te reverse of this on the other side. There is also about 1/2 mile of c&g on both sides of this road with about 20 entrances with curb radii to the west of this. We have a concrete sub that rented a Wirtgen curb machine with their early version of macjine control on it ?ÿIt uses a dxf file with a 2d line for alignment and a 3d line for grade of the front edge of the curb ?ÿ I have to set a hub at the beginning of each run for them to bench the machine on, then they go. ?ÿ

I dunno, 1/4" (0.02') for position seems excessively tight,?ÿ but 1/4" for the vertical it isn't unreasonable.?ÿ It's hardscape, and in some cases built to 0.3% grade (0.5% preferred).?ÿ If the grade is wiggling more than +- 1/2" stake to stake from design it could create minor ponding/reduced flow velocity, and joins with previously constructed minor structures may?ÿ cause?ÿ more severe ponding problems.?ÿ Tangent curb that wanders back and forth because of poor positioning can cause ponding too and looks ugly.?ÿ?ÿ

From a random DOT specification for curb and gutter stakes:?ÿ Setting Tolerance: "Stakes should be set within 0.03 foot horizontally and 0.02 foot vertically of the calculated position."?ÿ Finished work criteria (a random city specification):?ÿ "When a straightedge 10 feet long is laid on the top or face of the curb, or on the surface of gutters, the surface shall not vary more than 0.02 foot from the edge of the straightedge except at grade changes or curves."?ÿ?ÿSo if there's a 0.4"+- bump in a designed straight grade section exactly at your stake location; you will pay if the inspector's on the ball.

C&G work (actually, any hardscape) in flat country has to be staked tight and built accurately.?ÿ We all can see the difference when it rains; crappy design, staking and/or construction and there's huge shallow ponds covering a half a lane, 3" deep ponds at curb returns that take a day to dry, trash piling up in low velocity sections, etc.?ÿ If it's flat country, maybe a total station sprayout of C&G stakes from 500' away (or even worse, GPS only) isn't the way to go.?ÿ Yes, you can position your hub&tack?ÿ using a TS (or even GPS?, I'll contest that), but nail that elevation by getting out the level (& not the fiberglass rod, use a real rod); come from benchmarks and level the elevation on your hub tacks. Then look the inspector in the eye and say "Yep, +-1/4" vertical is my guarantee, any staking problems & I'll take ownership."

Please, anybody in the construction staking business doing delicate hardscape work tell me how GPS, or TS long distance radial stakeout techniques can actually meet the above specifications.?ÿ ?ÿCourtesy of Greg Helmer, Psomas & Associates, who first alerted me to the problems of GPS and 1,000 foot TS shots for precise local positioning surveying.

I didnt notice the last part of my post got cut off. The machine uses gps tied to the project control for location and a 1" total station for grade. They only go 200-300' from the robot before moving. If the concrete is good it works great. If not its a crapshoot.?ÿ

That's ridiculous for curb and gutter! I don't even know what else to say.

I once saw 160 feet of brand new curb ripped out because the line wondered by a quarter inch and the handicapped ramps were two tenths off by station so my concept of what truly constitutes ridiculous on this question may be a little different than typical.

The problem with tacking hubs for curb and gutter is that the guys will just hook their pocket tape on the back of the hub anyway, unless you leave the tack up enough to use for that purpose but then you run into folks unsure what to use for grade.

I don't tack my curb hubs unless requested, but if it is what the owner or their representative wants then that's what they will get, not too big of a deal in my view.

?ÿ

Wow

Usually C&G is anywhere within 4 tenths if they were being careful.

It has been a very long time since I've staked any C&G, but we used to set H&T every 25 feet on tangents and at 5-foot intervals IIRC on curb returns. And we leveled through them as well. Because the TS's we used back then weren't as precise as they are now, on the tangents we would set the end points via radial stakeout, set up over one end and BS the other and put 'em in as appropriate. From what I recall, we would also set the radius points whenever possible to provide a field check and re-set if necessary.

So as far as tolerances go, 0.02 +/- feet on C&G does not seem unreasonable to me but perhaps I'm seeing it from an old-school POV. For us, it was 0.01 foot +/- or we fixed it.

So you just put tacks in the center of each hub?

A good curb installer is the key. If you give an incompetent person precise control, they will still build an ugly curb. If you give a skilled builder loose control, they will still build a beautiful curb. That doesn't make it ok to do poor work, but the finished product is rarely the fault of the surveyor.

I saw an entire block of sidewalk get removed because of the 1/4" failure during an inspection.

The ADA rules have changed everything.

Did the inspector have enough knowledge to measure the 1/4"? Probably not since he used one of those carpenter levels with a slope display.

"C&G work (actually, any hardscape) in flat country has to be staked tight and built accurately."

Good post.

It's all about the grade.

In steep areas you can tolerate a lot of vertical error (but not at critical points) - heck you may even be able to use GPS.

If the design is for very low grades - you better get the vertical tight & right for all of the reasons listed in Mike's post. I cringe every time I see GPS being used to stake C&G, Catch Basins, Manholes, etc. on low slope projects - is it: I don't know or I don't care? Either way there will be places where the water won't flow as designed.

I give the 1" TS more credit - as long as you don't have heat waves it's vertically capable for 500'+. Keep it calibrated, use a short rod, double check all measure-ups, check into known control before and after: it's fast, accurate, and defensible.

The ADA standards as being implemented are within our measurement abilities, but they tax the abilities of builders.

I read 2% and, understanding significant digits see 2.49% gets rounded down to 2%, but they want to see to the hundredths and if it is 2.49% it exceeds 2% and it fails. Depending on the length of the run, the precision needed quickly approaches ridiculous. Additionally, it cannot be greater than 2% in any direction, and many municipalities are now requiring 1.5% for design because otherwise no one hits it. That is great, but in any direction means that the way it is constructed matters, and the engineers have to really noodle this stuff. The ADA is a YUGE, GINORMOUS hit to infrastructure budgets, both in retrofit and in moving forward. If someone told me that the ADA cost a Trillion dollars to implement, it would not surprise me.

These particular curb lines run at roughly a 2% slope...not exactly flat.

 Our normal historical procedure for staking curb is to set a 60d nail at 3’ o/s., 350’ maximum shots, no GPS. Horizontal limit .05’ and vertical read cut or fill to the nearest hundredth. This is all done off of good confirmed control.

I’ve watched the curb guys set their string-lines. It doesn’t exactly give me the greatest confidence in their respect for the staked points but have not once had a problem with curbing coming back to bite us...maybe because we generally don’t have very flat sites.