concrete and pipe

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Al Pike

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Honesdale, Pa
How do I deduct 4'' pvc and chairs from a concrete pour? I installed 2-4'' conduits 380' in a 27'' trench.With the chairs I needed about 13'' of concrete to give me 3'' above the pipes.The forman on the job ordered the concrete and came up with 39 yards and we were over about 19.
For future pours any information to help would make my world a better place.Thanks
 
I usually figure Length x With x Depth / 27.

380' length X 2' width x 1' depth = 760 cu ft / 27 = 28 cu yds.

The 2' width is the size of the backhoe shovel. and the extra 8 cu yards covers the sloppy excavation areas that might be larger.

How do others calculate concrete for encased duckbanks?
 
it would be hard to figure the cubic yards on a ditch like that. there are a lot of variables. if you average it out, it looks like you were using 1 cubic yd of concrete per 19' of ditch.
 
Unless I had a big, big ductbank, I never bothered calculating the takeout for pipe, let alone the chairs. Sloppy excavation will make up for you not calculating the takeout. A ductbank is not as concise as brain surgery.

Best Wishes Everyone
 
HighWirey said:
Unless I had a big, big ductbank, I never bothered calculating the takeout for pipe, let alone the chairs. Sloppy excavation will make up for you not calculating the takeout. A ductbank is not as concise as brain surgery.

Best Wishes Everyone
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Steve he ordered 39 yards and was over by 19 yards, thats a major waste of $.
 
mivey said:
But, it would appear the takeout was not the biggest problem.
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I am sure that will make difference to the person paying the bill. :wink:

I still feel it's wise to figure the pipe area so you know where you stand. It's always going to a be a relative issue, if the trench or form is ran tight then the pipe will make a big difference. If the trench is sloppy then the pipe will become a small issue.

We often do 8 to 12 - 4" PVCs in a duct bank and the company has done some very long duct banks with 64 - 4" conduits.
 
iwire said:
We often do 8 to 12 - 4" PVCs in a duct bank and the company has done some very long duct banks with 64 - 4" conduits.
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It's pretty amazing to think about the work involved with that...every 10 feet is 64 pieces of pipe to assemble and rack.
 
iwire said:
I am sure that will make difference to the person paying the bill. :wink:

I still feel it's wise to figure the pipe area so you know where you stand. It's always going to a be a relative issue, if the trench or form is ran tight then the pipe will make a big difference. If the trench is sloppy then the pipe will become a small issue.

We often do 8 to 12 - 4" PVCs in a duct bank and the company has done some very long duct banks with 64 - 4" conduits.
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In the example you provided, the takeout would be a big deal. In the OP's case it was about 3 yards (rough calc), meaning 85% of his problem was the calculation for the rest of the pour. Granted, 3 yards is still money wasted and I would not just skip the calc.
 
Just guessing, but I think you would only need about 9" of concrete to get 3" cover on the conduits. Based on a 27" wide 380' long ditch that would be 23.75 yd^3 minus the take out for conduit 2.5 yd^3 leaves 21.25 yd^3. This is about what you used.
 
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