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Burying Conduit

8K views 78 replies 15 participants last post by  itsnotrequired 
#1 ·
When trenching to bury a conduit, do you typically line the bottom with stone for drainage? Or do you just lay the conduit on earth and backfill the trench?
 
#4 ·
Depends on the soil. Also depends on if it's hand dug & backfilled or using a machine.
Really snotty and sharp fill I like to see some stone dust/etc.
 
#7 ·
30" is way deeper than required - but you can do it if you want. In clay, you probably don't need any "shade" fill under the conduit. That's really only necessary when the soil may shift and break the conduit.
 
#8 ·
If you're in Pittsville, then you only need to dig down about 20" -- 2" for the conduit, and 18" for the cover above it.

That last 10" you are digging is a waste of time and effort.

I'm in Parsonsburg, close by ;)
 
#9 · (Edited)
kbsparky said:
If you're in Pittsville, then you only need to dig down about 20" -- 2" for the conduit, and 18" for the cover above it.

That last 10" you are digging is a waste of time and effort.

I'm in Parsonsburg, close by ;)
It's a pain, yes. Delmarva Power's conduit agreement requires 2" conduit between 26-30" down. They also require special 36" radius long sweep 90s.

Anyone have thoughts on the ground water ponding in the trench? Issue, or no?
 
#10 ·
Ahh ... so NOW we learn the truth! You are installing your own trench/conduit for Delmarva Power! I understand the 30" depth requirement now. A great way to save some $$$ at the expense of a lot of sweat. :huh:

As for the groundwater in the trench, that is a given in many places here on Delmarva. With all the rain we have had this year, this is no surprise.

We did a similar installation in Eden last year, but since it was not as wet, water ponding in the trench as not a problem.

It won't hurt the conduits if you have to submerge them before backfilling. Just assemble them above ground before throwing them in ... :whistling2:
 
#11 ·
Anytime you trench in clay ground or any type that doesn't drain you're creating what is called a french drain. It will collect water at the bottom of it until the ground has time to resettle back to what it was before you dug...... and that assumes you back-fill it with the exact material you took out in the exact reverse.

Putting rock or other material in the bottom will do nothing if something isn't done to allow an escape for the water.

Only thing I would make sure is that the conduit is perfectly sealed. If water is capable of getting in and it can freeze the cable will be subjected to the pressures of ice on it while being confined by the conduit walls.
 
#13 ·
kbsparky said:
Ahh ... so NOW we learn the truth! You are installing your own trench/conduit for Delmarva Power! I understand the 30" depth requirement now. A great way to save some $$$ at the expense of a lot of sweat. :huh:

As for the groundwater in the trench, that is a given in many places here on Delmarva. With all the rain we have had this year, this is no surprise.

We did a similar installation in Eden last year, but since it was not as wet, water ponding in the trench as not a problem.

It won't hurt the conduits if you have to submerge them before backfilling. Just assemble them above ground before throwing them in ... :whistling2:
Saved about $500. Trench is 75ft long.

Wasn't sure about the water. My concern was the water finding it's way into the conduit. Water + power line = Uh oh. I guess it's inevitable though due to condensation. I was thinking about using stone to keep the conduit up off the bottom of the trench and away from any standing water. Thanks for all the info guys!
 
#15 ·
Speedy Petey said:
Water will find it's way in. It's expected. Water + power line = no problem.
I take it then, that if my long sweep 90s don't make full contact in the bell end of the pipe, that will be ok? See my attached photo. Because of the radius of the 90 and the distance it goes into the bell, it leaves a small gap on the bottom. This wasn't a problem on the other end of the run, because a coupling was used to connect the 90 to the pipe.
 

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#18 ·
Speedy Petey said:
Shouldn't be. As long as it stays together.
I might have used a bit more glue on that joint.
I actually had quite a bit of cement on the elbow and inside the bell. I think the large radius of the elbow combined with the depth of the bell contributed to the gap. (A curved piece mating with a straight piece) I suspect that the end of the elbow made full contact somewhere inside the bell.
 

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#19 ·
I actually had quite a bit of cement on the elbow and inside the bell.
Some inspectors here insist on seeing excess squeezed out of the joint - that way it is visually confirmed that it's fully glued. I'm not sure that's an enforceable requirement, but it is good practice. It's impossible to use too much.
 
#20 ·
mpoulton said:
Some inspectors here insist on seeing excess squeezed out of the joint - that way it is visually confirmed that it's fully glued. I'm not sure that's an enforceable requirement, but it is good practice. It's impossible to use too much.
I put a light coat in the bell and two fairly liberal coats on the pipe/elbows. Think I'll be alright or should I relay some new pipe?
 
#25 ·
Pittsville said:
I take it then, that if my long sweep 90s don't make full contact in the bell end of the pipe, that will be ok? See my attached photo. Because of the radius of the 90 and the distance it goes into the bell, it leaves a small gap on the bottom. This wasn't a problem on the other end of the run, because a coupling was used to connect the 90 to the pipe.
Just curious... but you guys HAVE seen this issue in the field, right? Where a large radius sweep leaves a gap in the bell because of the bell depth?

I was talking to an electrician earlier today who stated that he's never seen this problem. He asked about the sweep and when I explained that both ends have spigots, he said I should either be using a sweep with a belled end or making the connection to the conduit with a standard coupler. A gap wouldn't be left that way because the connection wouldn't be as deep as the bell on the conduit? If he's right, whats the point of being sold a sweep with two spigot ends? lol...
 
#27 ·
kbsparky said:
Where did you obtain such a sweep elbow? None of the ones I have ever bought have bells on the ends ....
That's just it... my sweeps do NOT have bells. So therefore, you either have to insert the end into a coupling or into the bell on the end of a length of conduit, which leaves the gap. The electrician was the one who said I needed sweeps with bells on them.

So when YOU install large radius sweeps, how do you connect it to the straight conduit? If you fit it with the bell of the conduit, have you noticed the gap?
 
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