Broken U/G conduit.... am I missing something ?

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brantmacga

brantmacga

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Location
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Former Child
I have a project that involved intercepting two existing 4” PVC conduits underground, install a handhole at that point, and continue on to my new service equipment.

Each 4” terminates at separate padmount transformers that sit next to each other. I’m only pulling cable through one of the conduits.

Last week, I blew the conduits out and noticed something very odd. We blew about 300 gallons of water not just out of the other end of a single 4”, but out of all three open ends. Ok so imagine two parallel conduits with 90’s on each end; blow a single 90, and you get air/water out of the OTHER conduit on BOTH ends. These conduits are roughly 430’ end to end, half under pavement. Doesn’t matter which conduit you blow, you will always feel air at the other 3 open ends. There is no handhole or junction box anywhere. We blew a string line through it.

I told the GC PM that there is a break somewhere with an open cavity around it, and it needs to be scoped. They discussed and said to me they think somehow we are just drawing air through the other transformer cabinet.

Alright, am I a crazy person? Am I missing something obvious? I tried to locate the break with my fish tape connected to a locate tool transmitter, but almost all of this conduit run is trenched with another 8 sets of parallel feeders and it overpowers my locator.

It’s been kicked to the architect as to wether or not we should attempt to pull the feeder. My position was to have it from them in writing acknowledging that I think it’s broken and not responsible for damage to the conductors. But I just feel like everyone is looking at me funny when I say the conduit is broken and that it’s completely normal to have air coming out of the other conduit.


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I agree with you. It’s broke somewhere.
Do this. Cap one end of a pipe. Blow from the other end. See what happens.
I know you said no handhole or box, but...
Sure sounds like it
 
Tried that.... cap one end, it just blows harder out the other conduit.

Thought about a buried box, but the fact we got a string line through made that less probable to me.

Idk what else it could be. I mean I think it’s broken just throwing this out for any other ideas I hadn’t considered.
Thanks all.


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I wonder what would happen if you plugged all of them and pressurized. Might blow out where the break is?
Unless the break is under pavement.
 
brantmacga said:
Tried that.... cap one end, it just blows harder out the other conduit.

Thought about a buried box, but the fact we got a string line through made that less probable to me.

Idk what else it could be. I mean I think it’s broken just throwing this out for any other ideas I hadn’t considered.
Thanks all.


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Click to expand...
Are there “As Built” prints you can access from location owner, or from contractor that did the original install?
If not a box in line, possibly a spot where multiple conduits were damaged in one spot allowing water and air to pass through a small cavity?
I would anticipate some water, but air through other conduits? Sounds sketchy.
 
Add me to the buried box column. IMO there is no way a set of broken conduits in the ground allow air to flow through all of them simultaneously.
 
brantmacga said:
Tried that.... cap one end, it just blows harder out the other conduit.

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Click to expand...

That alone should have thrown a red flag for the GC PM and that it’s not “drawing through another transformer” that statement doesn’t make sense anyway..
 
infinity said:
Add me to the buried box column. IMO there is no way a set of broken conduits in the ground allow air to flow through all of them simultaneously.
Click to expand...

I could see if if a backhoe has popped the tops on the set of conduits. Maybe not broken all the way in half, but enough to do what he is talking about.

I have dug some out to repair where a sub has dug into ours.. they tried to “fix” it. They popped a piece off one or two pipes and cracked the others pretty good. They cleaned everything up and laid a board over the conduits, then back filled..
 
Bluegrass Boy said:
Are there “As Built” prints you can access from location owner, or from contractor that did the original install?
If not a box in line, possibly a spot where multiple conduits were damaged in one spot allowing water and air to pass through a small cavity?
I would anticipate some water, but air through other conduits? Sounds sketchy.
Click to expand...

Already working off as-built, it shows straight run to transformer.


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brantmacga said:
Blown with air compressor


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Click to expand...
That would further back my thoughts of a burried box or hand hole you obviously have enough pressure to blow out whatever water was in there. With that amount of air pressure a string could easily find its way in a conduit through a box. My next question would be is the string in the same conduit on both ends?

Another words the same of conductors on both ends? Of conduit the string is in?

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infinity said:
Add me to the buried box column. IMO there is no way a set of broken conduits in the ground allow air to flow through all of them simultaneously.
Click to expand...

In Georgia you have to keep a real open mind about thing like this. There is no telling what you may find. It wouldn't surprise me if the conduits are sticking into a culvert someplace,
 
brantmacga said:
Blown with air compressor


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Probably not a little 3 gallon tank compressor with a 1/4" hose I'm guessing?

What did you use for a piston to blow it in with? Actual foam piston for fishing conduits or a plastic bag or other makeshift item that may find it's way more easily into a conduit leaving a concealed box than what a foam piston might do?

Does pulling a mandrel of some sort back through ever hang up anywhere during the pull?

Broken conduits that are direct buried wouldn't likely have such easy air flow continuity between them unless something surrounds them that would keep any fill from seeking it's way into the gap.
 
kwired said:
Probably not a little 3 gallon tank compressor with a 1/4" hose I'm guessing?

What did you use for a piston to blow it in with? Actual foam piston for fishing conduits or a plastic bag or other makeshift item that may find it's way more easily into a conduit leaving a concealed box than what a foam piston might do?

Does pulling a mandrel of some sort back through ever hang up anywhere during the pull?

Broken conduits that are direct buried wouldn't likely have such easy air flow continuity between them unless something surrounds them that would keep any fill from seeking it's way into the gap.
Click to expand...

No, just ran a rag through as a rabbit.

But you’re right, i need to pull a piston through. That should give me a clear answer.

Thanks !


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Here’s a screenshot of plans that shows my conduit run.

This line was taken from as-builts.

You will notice there is an outline of a box about 150-ish feet in from the right side. I’ve already dug that up and nothing is there.

I was told that was the location of an old existing padmount transformer, and they didn’t turn off the CAD layer for that object when finalizing the drawings.


fb68b8ed2bbf2bec5378f90f3d691bed.jpg



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