# Underground Work



## Ninjazx916r (Apr 1, 2011)

Had a run in with the engineer recently. I want to see what your thought about this. 

When you lay underground schedule 40 conduit. What is the purpose of putting sand around the conduit? Also, will slurry be better? What about concrete since it has aggregates in it that might penetrate through the conduit? Is shading for protection when future construction is digging near the conduit? Or is it for vibration and earth movement?


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## macmikeman (Jan 23, 2007)

Much ado over nothing. Make sure to glue the joints well cause that is what becomes a problem on buried runs of pvc. Would love to see some proof of rocks moving about in buried soil damaging conduits. Yes I am aware of codes, ordinances, and power company rules in various places prohibiting backfill containing rock material. It's another ''might happen'' scenario that goes unproven.


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## telsa (May 22, 2015)

Ninjazx916r said:


> Had a run in with the engineer recently. I want to see what your thought about this.
> 
> When you lay underground schedule 40 conduit. What is the purpose of putting sand around the conduit? Also, will slurry be better? What about concrete since it has aggregates in it that might penetrate through the conduit? Is shading for protection when future construction is digging near the conduit? Or is it for vibration and earth movement?


Since we're in the same area code... I'll explain local conditions and obsessions.

1) Down in the valley the digging is pretty easy -- until you hit about 4 feet down -- the hard pan. It's as forgiving as concrete -- and chips out just about as fast.

2) Up in the foothills, the digging is pretty rotten -- once you've scratched the surface you're into caliche.

https://en.wikipedia.org/wiki/Caliche

THIS is the threat to PVC. So it's necessary to 'bed' the PVC -- and all other pipes, BTW, in sand.

Decomposed granite is not to be used. It simply will not compact well. The result is that the soil is destined to subside if decomposed granite is used.

[ For electricians from other parts of the nation, Sacramento has decomposed granite left over from the glacial age everywhere to hand. This makes it the cheapest (unwanted) back filling material you can imagine. ]

After your PVC is bedded, it needs to be topped over with SAND. SMUD and PG&E and Roseville Electric all hate native backfill directly around their pipes.

Once you've covered the pipes with a decent cushion -- the rest of the way native backfill is acceptable -- IF it's largely stone free. 2" stones are the upper limit in most trenches (the big massive ones, ie wet trenches) with small trenches usually restricted to 3/4" minus, screened material.

This sequence means that for ever afterword, getting back into your trench will be practical with even hand tools or a hydro-vacuum machine. 

The caliche out here utterly destroys the toughest digging teeth the equipment industry is able to manufacture ! Anyone that sees them torn up is drop jawed. The strongest backhoes -- scratch the surface -- like it was a solid concrete mass.

Caliche is nature's concrete.


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## dmxtothemax (Jun 15, 2010)

I thought the sand was to let water
run off, like a drainage channel.


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## backstay (Feb 3, 2011)

I've never seen a failed PVC underground run that was caused by a rock. Landslides or digging only.


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## pete87 (Oct 22, 2012)

Sand is used to " Pack Tight around PVC so it will not settle ...

also creates a barrier to Rocks getting pressed against the PVC .


Called for in Specks ... Usually .




Pete


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## varmit (Apr 19, 2009)

Sand fill:
Helps prevent rock penetration- either during backfill or over time.

An underlayment of sand will make it easier to level the pipe if the ditch is not perfect. This helps to eliminate excess up and down bends.

If there are multiple layers (or runs) of conduit, an initial sand backfill will prevent crushing the duct bank "chairs" during final backfill and allow the spacing to remain intact.


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## splatz (May 23, 2015)

Even if you do everything you're supposed to, conduits are often compromised. When that happens, if there's anyone other than Mother Nature to blame it on, there will be hell to pay. So whether or not I think sand is effective protection, I'd be putting it in so there's no finger pointing if it ever fails. 

Seeing how concrete sonotube piers get heaved around, there's no doubt in my mind that putting some space between the rocks and the pipes with sand is a good idea.


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## ralpha494 (Oct 29, 2008)

It's also a nice warning for the backhoe operator, years down the road, that he's about to find the pipe you buried.


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## joebanana (Dec 21, 2010)

It's to keep the conduit from flattening out when the back fill is compacted. That's what I heard.


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## Dash Dingo (Mar 3, 2012)

I do it so the pipes don't get damaged durning the backfill if excavators are driving over it.
It acts as a cushion.


Sent from my iPhone using Tapatalk


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## backstay (Feb 3, 2011)

ralpha494 said:


> It's also a nice warning for the backhoe operator, years down the road, that he's about to find the pipe you buried.


This might help.


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## catsparky1 (Sep 24, 2013)

I have dug in California and Some places want It some don't . Rocks in the ground have no factor on sand when shading or bedding . I have dug in Hawaii No sand required . As far as digging goes Hawaii wins hands down over anything else we have ever torn into . Yeah hardpan aint no joke but that rock is flipping brutal digging .


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## macmikeman (Jan 23, 2007)

catsparky1 said:


> I have dug in California and Some places want It some don't . Rocks in the ground have no factor on sand when shading or bedding . I have dug in Hawaii No sand required . As far as digging goes Hawaii wins hands down over anything else we have ever torn into . Yeah hardpan aint no joke but that rock is flipping brutal digging .



Sand is often specified for underground trench backfill around this state, by Heco, govt specs, and around Kailua Oahu where a certain city inspector has his jurisdiction...


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## AK_sparky (Aug 13, 2013)

I've seen issues where deep frost and truck traffic have pushed rocks into pipes.


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## pete87 (Oct 22, 2012)

Damm ... the Best you can do is use PVC with the Bell Ends ...

Way better than the Couplings ... and seat the pipe ... use the cleaner 

with the glue .





Pete


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## drumnut08 (Sep 23, 2012)

Ninjazx916r said:


> Had a run in with the engineer recently. I want to see what your thought about this. When you lay underground schedule 40 conduit. What is the purpose of putting sand around the conduit? Also, will slurry be better? What about concrete since it has aggregates in it that might penetrate through the conduit? Is shading for protection when future construction is digging near the conduit? Or is it for vibration and earth movement?


 Engineers create problems where there usually aren't any . Clean fill ( no rocks , no clay, ) is all I've ever seen in NJ specs . I've seen guys (plumbers ) pull the worst garbage soil out of the ground and try to reuse it . It's always funny when the guy comes out to do his soil compaction test , and it fails miserably , lol ! I've done a nice clean sand bed for direct burial medium voltage cable ( 13,200 VAC) , but If it's in the job specs to have a sand bed around the conduits , arguing with the engineer will usually not go in your favor . If job specs supersede the NEC , that's not up to the inspector to make the call on an engineered job . I used to finesse them early on along with the inspectors . Kindness Goes a long way with these guys . Good luck !


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## 3xdad (Jan 25, 2011)

Bird dog said:


> ....


Gesundheit!


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## 220/221 (Sep 25, 2007)

I'd say that the specifications for sand are written (like many rules) to take individual judgement out of the equation.

I've trenched and installed _I don't know how many_ miles of PVC in my life and I understand exactly what is required for a good installation. 

Soil conditions are very different and will require some common sense and experience. 

PVC is pretty tough but in some areas here, we have rocks that could damage it. In these cases you chuck them off to the side, shade the conduit by hand and then continue with machinery. 

In other areas, the soil is perfect and it would be a waste of resources to use any kind of fill other than what you dug up.

In a half and half kind of soil like decomposed granite + boulders, you could easily use machinery to fill as long as someone was working the trench and keeping an eye out for the occasional boulder.

Bottom line: It covers more asses to specify sand rather than specifying "use your damn head and don't do anything stupid"


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## Jarp Habib (May 18, 2014)

telsa said:


> Since we're in the same area code... I'll explain local conditions and obsessions.
> 
> 1) Down in the valley the digging is pretty easy -- until you hit about 4 feet down -- the hard pan. It's as forgiving as concrete -- and chips out just about as fast.
> 
> ...


Ahhhh, 916. I still remember Dad renting a Bobcat with auger attachment to dig 4 postholes and using a backhoe to grade Mom's flower bed. 

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