Minimum thickness of "sand" around pvc conduit and To compact or not compact the sand for pvc in trench

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sparky1591

Member
Location
Mississipi
Occupation
Electrician
We are laying about 50 ft of PVC (1'' conduit) in a trench. We are going to sift the material that we took out and put it back around the conduit.

Question is what is the minimum thickness should the "sand" cover all around the conduit? Does the "sand" need to be compacted? If yes at what compaction percentage? Wet compaction or dry compaction?
 
I generally put down about 3-4'" of sand before laying pool pipe or conduit. Then another 4" or more on top, then the spoils from the excavation.
Caution tape on top of sand before the spoils. If the spoils are clean, I may not use sand at all. Most of the time I'm dealing with rocky soil.

I may wet the sand to get it settle around everything and pack it tight. No matter how much compacting, stamping, etc.. you do, the trenched area will settle. Just let your customer know this.
 
Mystic Pools said:
I generally put down about 3-4'" of sand before laying pool pipe or conduit. Then another 4" or more on top, then the spoils from the excavation.
Caution tape on top of sand before the spoils. If the spoils are clean, I may not use sand at all. Most of the time I'm dealing with rocky soil.

I may wet the sand to get it settle around everything and pack it tight. No matter how much compacting, stamping, etc.. you do, the trenched area will settle. Just let your customer know this.
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Nice.
I like to place the caution tape a bit higher. 6"-12" below the finished grade just to give the conduit a chance with aggressive excavators;).
 
Mystic Pools said:
I generally put down about 3-4'" of sand before laying pool pipe or conduit. Then another 4" or more on top, then the spoils from the excavation.
Caution tape on top of sand before the spoils. If the spoils are clean, I may not use sand at all. Most of the time I'm dealing with rocky soil.

I may wet the sand to get it settle around everything and pack it tight. No matter how much compacting, stamping, etc.. you do, the trenched area will settle. Just let your customer know this.
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Advantage of sand is when digging the sand is an good conduit locator
 
tom baker said:
Advantage of sand is when digging the sand is an good conduit locator
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Won't work here in the sandy soils we have in certain locations here. Guess need to bring in some heavy clay and pack that around the conduit before filling in with the sand that was originally taken out :unsure:

good protection from aggressive excavators could be pouring concrete in bottom of trench, encasing your conduit.

I've generally found caution tape to only be useful for telling you what you have already likely hit, if you didn't expect anything to be there. Might be useful for telling you you are getting close if you are carefully trying to find something you know is there.
 
ptonsparky said:
Caution tape makes inspectors happy, that’s about all.
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Recent years there is so much (not just electric) getting directional boring or plowed into place and I haven't seen any tape utilized with those methods. I could see it being possible with plowing but not so much for directional boring.
 
Some jobs will have specs for how much sand. A lot of the jobs I bid it shows 6” sand below and above the conduit. That would be clean sand, not sifted spoils.

If that is not spec’d, I will use the spoils unless it contains large rocks. If it does, I’ll bring in fill. But we don’t have a lot of rock where I work.

As far as compaction, evenly graded material, like sand, 3/8” pea gravel, #3 drain rock, etc, goes in around 90% compaction just pouring it in. You’re not going to get a whole lot more.

When I use sand, I’ll pour it in, grade it out, and then add a lift of compactable fill and hit it with the compactor.

I put caution tape in all my ditches, but it goes 6” below the surface. I dig to 24” most commonly, as that gives me a little flexibility, and gives me the required 18” from the top of the conduit. Then I’ll get a lift or two of fill, roll the tape, and final grade and compaction.
 
if you are compacting the back fill, sand is a good idea. If you are pulling a mandril to get it approved, sand is a good idea. If neither of those 2 apply, just don't have rocks in the backfill. I one time had a 4" PVC get dimpled by a rock on a utility side conduit, it stopped the mandril. Luckily for me it was about 24 inches from the vault and you could reach in and feel it, the inspector passed it because it was minor. Had that of been four foot in, we would have had to dig up the street 4-1/2' deep.
 
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