Paving reverse curves 1

[ACtrafficengr]

I was discussing superelevation with a construction inspector the other day, and he mentioned that the designer had specified curve transitions that most pavers cannot achieve. This is what I call an "evolved" road, a paved horse-drawn wagon track, as opposed to a properly engineered road. The alignment is tortuous in some areas, and realignment was not in the budget.

So, my question is this: what rate of change in cross slope can a paver resonably be expected to pave? Say, in units of % cross slope per 100 feet or some such.

This leaves aside the question of what rate of change is advisable. IIRC, the Green Book does have some guidance on that.

Thanks!



"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[civilperson]

Run out of 2% crown section, 50 ft: elevate or depress one side to create 2% superelevation, 50 ft: and then 50 ft per 2% additional superelevation. Same distances for transistion back to normal crown section. This assumes speed less than forty MPH. Hairpin curves in the mountains do the warping in about 1/3rd the stated distance,(need shoulders).

 

[civilman72]

The most important design parameter to answer your question is design speed.

At low design speeds (<30 mph) I've found that a super transition of 1% per 10' is smooth, and can be done in as little at 5' (but would only recommend at intersections).

FYI - A 1% change every 10' would fall in line with what civilperson stated for mountainous terrain.

 

[ACtrafficengr]

With due respect, I'm not talking about design speed. I'm talking about paving machines.

For example, at one location, the designer shows the super going from 6% right to 6% left in 125 ft. Now, I know this isn't a good design, but assuming for whatever reason you wanted to build it, could you? Or would you run out of screed adjustment on the paver?

Thanks!

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[ACtrafficengr]

PS: No, we didn't build it per plan.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[civilperson]

The change in superelevation is easily built if the subgrade is built correctly, (no change in pavement thickness is required or desired).

 

[ACtrafficengr]

Ah - that's the problem. The existing super was way out of whack. We recycled with foamed asphalt, and I guess there is a limit to how much x-slope correction you can get with that process.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[eea]

ACtrafficengr,

Reaction of the hydraulics of the machine should be fairly instantaneous. The Blaw-Konx Paving Manual says the grade sensor will react to 0.03” of grade change. I have a hard time imaging that you can’t dial in whatever cross slope is needed. Did the Contractor consider slowing the paver down to allow more time for the screed to react? I suppose that the amount of material head in front of the screed will have some effect, but there is no limitation stated in the manual.

I’m guessing they are probably running grade off one ski? They can always double ski’d and run automatic slope control for the cross slope to more accurately follow the existing pavement. One thing I know for certain a Contractor never wants to do is “bottom out” or drag the screed. They will always try to run heavy on the mat and won’t want to dial in the cross slope until well past the transition points to avoid it.

If your question is can the machine do it, yes. Does the Contractor want to do it, probably not. I try to specify milling and leveling binder for crown correction on my projects. Even then, you’ll still find the screed man gun shy about dialing in super-transitions.

 

[eea]

Addition:

I missed the mention of -6% to 6% in 125'. The manual gives a cross slope operating range of 10.45%, I assume that to be full throw from -10.45 to +10.45. I know I've dialed in -2% to +9% before.