How much weight on top of underground conduit?

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Coppersmith

Coppersmith

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Tampa, FL, USA
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Electrical Contractor
I'm currently working on running 1" PVC underground conduit to a new above ground pool installation. The conduit needs to emerge at the far end of the pool and the straight shot takes the conduit under the pool. The conduit will be 18" down. There will be pavers installed under the pool.

Is there any reason I should not run under the pool?
 
680.10 isn't about how weight on the raceway will affect it, though it is something that must be complied with.

the weight per square foot of the base of the pool isn't as much as one might think though.

Someone correct me if I am wrong, but wouldn't 40 inches deep water in the pool exert 40 inches of water column equally across the entire bottom of the pool? I also believe you would likely apply more force to the conduit if you used a mechanical compaction machine when backfilling the trench then this static load would ever exert on it.
 
kwired said:
680.10 isn't about how weight on the raceway will affect it, though it is something that must be complied with.

the weight per square foot of the base of the pool isn't as much as one might think though.

Someone correct me if I am wrong, but wouldn't 40 inches deep water in the pool exert 40 inches of water column equally across the entire bottom of the pool? I also believe you would likely apply more force to the conduit if you used a mechanical compaction machine when backfilling the trench then this static load would ever exert on it.
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And with all that said 680.10 answers this question "Is there any reason I should not run under the pool?"

Roger
 
Hmm, isnt it 680.11, which says it should not be under pool unless required by... and if so must be under the 300.5 cover depths requirements, so that is what, 18 inches under the pool after compaction? not too much into it but in my own code book it is 680.11
 
Adamjamma said:
Hmm, isnt it 680.11, which says it should not be under pool unless required by... and if so must be under the 300.5 cover depths requirements, so that is what, 18 inches under the pool after compaction? not too much into it but in my own code book it is 680.11
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In the 2017 NEC it is 680.11 before that it is 680.10

Roger
 
roger said:
And with all that said 680.10 answers this question "Is there any reason I should not run under the pool?"

Roger
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Wellll, maybe I should looked more carefully, seen the burial depth chart right away and never really read the text that carefully.

How deep before you can say it is no longer under the pool - once past the core of the earth?:cool:
 
kwired said:
Someone correct me if I am wrong, but wouldn't 40 inches deep water in the pool exert 40 inches of water column equally across the entire bottom of the pool?
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If I am remembering correctly from the instrumentation class I took, each square inch column of water exerts it's force straight down and does not exert force to the sides. Of course, there are other columns of water on each side of the one we are discussing that are also exerting their force straight down. It doesn't matter the size of the column, the force is the same at any point on the bottom (as long as the depth is the same).
 
OK, so I'm supposed to stay five feet away, however the pool has a built-in motor with a wiring compartment so I have to run the conduit into that. Do I have to approach it at a right angle in order to stay five feet away as much as possible, or can I approach the compartment at a more obtuse angle meaning the conduit will be within five feet for a longer distance?
 
Coppersmith said:
If I am remembering correctly from the instrumentation class I took, each square inch column of water exerts its force straight down ...
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Not so. Fluids exert a force in every direction. The keel of a submarine's pressure hull encounters (essentially, less ρΔz) the same pressure as its deck and sides.

And to a reasonable approximation -- good enough for small-scale engineering & construction purposes -- soil is a fluid.
 
Coppersmith said:
If I am remembering correctly from the instrumentation class I took, each square inch column of water exerts it's force straight down and does not exert force to the sides.
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That is what I understand.

drcampbell said:
Not so. Fluids exert a force in every direction. The keel of a submarine's pressure hull encounters (essentially, less ρΔz) the same pressure as its deck and sides.

And to a reasonable approximation -- good enough for small-scale engineering & construction purposes -- soil is a fluid.
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With the submarine the pressure should be less on the upper portion of the hull then it is on the bottom larger the vessel the more noticeable this may be.
 
kwired said:
That is what I understand.

With the submarine the pressure should be less on the upper portion of the hull then it is on the bottom larger the vessel the more noticeable this may be.
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Pressure in salt water increases by 1ATM every ~33' of depth, but here's a thought experiment: If a submarine is 33' from deck to keel and you run a pipe through it from top to bottom open to the sea, will water continually flow through it due to the pressure differential? I think not. Or maybe I have discovered a source of free energy. :D
 
would only work if your sub was three times that fat.. roughly 100 feet... to get enough water movement to actually create scrw motion, if I remember the experiments... but once they figured out how to create power from nuclear energy the technology was not used anymore in experiments. a version of one of the methods they tried became the basis for some of the tidal energy systems that they have been trying to make, using a flapper to create energy, attached basically to a cork or bobber. In fact, they even were trying to create a method of allowing the seal teams to transition in and out of such a hole from either top or bottom of subs, including underwater sled parking, so that the subs did not have to surface to release the seal teams off of a coastline such as Korea... but in early eighties they still had not come up with a great version of that, even with the James Bond movies for inspiration. Lots of interesting things in first year of sub training in Dago...lol..wonder if that is gone like the rest of the base was last time I went there on a visit.
 
kwired said:
... With the submarine the pressure should be less on the upper portion of the hull [than] it is on the bottom ...
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Right you are. The pressure on the keel is greater than the pressure on the deck. This pressure difference can be calculated as the density (ρ) of water multiplied by the difference in depth (Δz).

If the pressure hull is ~10 meters high, this difference is about one atmosphere, which is essentially nothing when compared to the ambient pressure at maximum dive depth.

It's even more irrelevant in the case of underground conduit.


ggunn said:
... If ... you run a pipe through it from top to bottom open to the sea, will water continually flow through it due to the pressure differential? ...
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A submarine is not needed for this experiment. All that's required is a submerged vertical pipe, open at both ends.
There will be no flow. Although there is a Δp between top & bottom, there is exactly the same Δp in the ambient water. This is why a whale doesn't have a blood-pressure crisis when making a vertical dive, even though the blood pressure in its brain is 2000 mmHg greater than in its tail.
 
drcampbell said:
A submarine is not needed for this experiment. All that's required is a submerged vertical pipe, open at both ends.
There will be no flow. Although there is a Δp between top & bottom, there is exactly the same Δp in the ambient water. This is why a whale doesn't have a blood-pressure crisis when making a vertical dive, even though the blood pressure in its brain is 2000 mmHg greater than in its tail.
Click to expand...

It was a joke.
 
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