In our neck of the woods our site plans and storm water management requirements are vastly more complicated than similar projects 10-15 years ago. We might have 4 different curb types for even a small commercial build. Difference from top of curb could be 4?, 6? or maybe 8?. We try to have spot elevations calling out both Top & Flowline on our grading plans but space on plans does not always allow.?ÿ
Seems to me if I had to pick one for the plans I would like to see Flowline. That allows ?ÿyou to easily analyze drainage regardless of curb height.
Convention of most curb & gutter contractors has been to request cut/fills to the Top back of curb. Although some have specifically requested cut/fills to Flowline.?ÿ
I like the latter. In almost all cases the Flowline is the most critical aspect of the curb & gutter.
So to the chagrin of my boss I have been labeling only Flowline elevations for my plans that are 30 scale or larger. And staking them in the field to Flowline as well. The lath are clearly labeled ??3?? offset Back of Curb, Cut/Fill to Flowline?. I verbally inform each contractor and provide them with a stakeout map clearly stating that. No problems yet other than a low grumble from the boss man.?ÿ
Just wondering if anyone else uses a similar method. Or what is conventional for your region.?ÿ
Typically the staked call is to TBC (top back curb) with 3' offsets. Although some contractors have machines that make use of 4' offsets. I've never seen nor had a request for calls to the flowline. Even valley pan was staked to the edge of concrete not flowline.
Face of curb horizontally, both top and FL for elevation. In most cases it's a standard 0.5' difference but in a transition to matching existing the difference will vary.?ÿ
Around here they want TBC, usually 3ft offsets. Done work in other states (notably CA) where they wanted top face of curb, and on rare occasion flowline.
In the end, everyone on site is looking to have to do the least amount of work with the least amount of liability.
We try to have spot elevations calling out both Top & Flowline on our grading plans but space on plans does not always allow.
I don't trust any planset with a 3D linear feature that only has random spot elevation callouts. The best planset is one that comes with an alignment and profile for each flowline, with stations calling out curb type transitions and any other critical points. But if that isn't given, I will create one myself so can both check that the grades work with the spot elevations, and have something that I can be flexible with in the field.
Then it's as easy as dropping the align/profile in the DC, meet with the super and contractors, figure out what they need and what offsets work best, then just run down the alignment applying whatever H/V offsets for top/face/back plus construction offsets to get to my stake mark.
OP buried the lede on that one. His contractors read plans AND are flexible??ÿ
Flow line only, in Minnesota never had anyone ask or tell me they prefer Top Back. Agree that flowline is most important part.
Seems more and more contractors requesting 4?? offsets, curb guys don??t seem to mind and higher chance they don??t get wrecked during the grading!
In the miles of curb and gutter I have staked it was always TBC with single and/or double offstes if any. ?????ÿ
buried the lede
Had to look that one up:
A lede is the introductory section in journalism and thus to bury the lede refers to hiding the most important and relevant pieces of a story within other distracting information. ... In journalism, the lede refers to the introductory section of a news story that is intended to entice the reader to read the full story.
Typically the staked call is to TBC (top back curb) with 3' offsets. Although some contractors have machines that make use of 4' offsets. I've never seen nor had a request for calls to the flowline. Even valley pan was staked to the edge of concrete not flowline.
Yep, TBC is the fiduciary mark.?ÿ I've staked dozens of miles of curbs, for hand forming with batter boards and they want offsets on long curves, tight stuff at the drainage grates and around curb returns and it turns out great.
I've set control for extruders ("string lines") and they tell me they only need point to point vertical control because the machine has tracks for wheels and automagically introduces vertical curves where needed.
Balderdash!?ÿ Extruders work good on straight grade curb but are woefully bad at curved curb with changing grades.?ÿ Our job is to provide TBC at reasonable intervals and if it's screwed up that's on the concrete former.
I learned long ago never to assume the contractor's people can actually read for comprehension.?ÿ
I like the latter. In almost all cases the Flowline is the most critical aspect of the curb & gutter.
?ÿ
Probably just need to leave this up here.?ÿ ????ÿ
'Round here, ADA ramp requirements make TBC critical. If the slope of the concrete from curb to top of ramp is greater that 2%, it will have to be ripped out and replaced. A lot of inexperienced concrete firms have been burned by this.
When calculating curb elevations, my simple brain has a hard time switching back and forth from flowline elevations to top back of curb elevations at ramps. I've come to default to calculating TBC to minimize my mistakes.
Sometimes, edged of gutter/EP, flow line, and TBC all have elevations called out on plans. It's simpler for me to layout TBC and let the curb guys figure the rest out.
I've?ÿ never had a set of plans that gave flowline elevations.?ÿ My plans must have all been prepared by the low bidder.
In my experience (GA, SC, NC) a 3?? o/s BOC is the convention, but recently on a job with curb machine for whom their in-house surveyor provided a 1.5?? o/s along with an elevated 1?? o/s because the guys pinned the string to those offsets, so I did the same. They didn??t have to put a level and ruler on anything. So I conformed because I figured on getting better results. Obviously, there was a risk of wiped out stakes, but we established a good working relationship before I committed and all was well.
But one day all of my stakes got wiped out, and an as-built revealed errors in their work as much as a tenth, as they, coincidentally, were training a kid on the curb machine. Everything functioned, but I learned my lesson. Never sacrifice trust on the altar of accommodation.
As for the point of the OP, and related to the aforementioned, there is a reasonable expectation of competency in the performance of work by construction professionals for which the flow line is directly related to the top back of curb, per construction plans and details. Apart from showing breaks from standard to spill cubs, or transitions to a roll curb, handicap and such, the flow line follows.
The flow is key but it has a direct relationship to the back, top of curb.
When designing kerb I've always used top face/front as the reference on the long section, and used this point for my set out aswell, the reason for this is because the string line for concreters kerb machine is referenced to this point. This method keeps it consistent and reduces confusion, the peg references top face, the long section references top face, the stringline references top face, road widths are measured face to face.
The designer should take into consideration the height of the kerbs when transitioning between different profiles to ensure that there is continuity between the two flowlines. In saying all this, it's easy when you're responsible for design and construction.
