protecting pipe in trench

Dansos

Member
I wanted to get some feedback and/or thoughts on this job. We trenched approx 55' of asphalt in a school parking lot. When digging the trench I noticed a lot of ash and/or rock under the asphalt and I am getting a little worried about how we are going to back fill and make sure we protect our piping. My thoughts are to either:
A. Install a bed of sand on bottom of the trench, lay our pipe (1" PVC Conduit) on the sand and put a layer of either 2b stone or something of the like over it.
B. Was also thinking of running our pipe through RMC to give it extra protection. (overkill? bad idea?)
I just do not want this to be a problem for us down the line if the piping ever gets damaged or crushed. This is not an area that I am well versed in....
PS- Our trench is currently 28" deep so we can put something down and still maintain our minimum 24" depth from top
 

infinity

Moderator
Staff member
I would use sand around the conduit. 300.5(F) would prohibit rocks and other debris from being in contact with the PVC where it could damage it.
 

Dansos

Member
thats what I figured. I was originally going to remove the asphalt and use a ditch witch to make our trench as narrow as possible, but I figured making it wider would allow us to have some room to work as well as making sure if we did hit anything hard we had room to dig by hand. I didnt really think about back filling until after the fact.
 

hbiss

EC, Westchester, New York NEC: 2014
28" is plenty deep. You might want to use sched 80 PVC which is heavier. 4" sand under, 6" sand on top then compact and fill the rest of the way with Item 4 or whatever to allow for repaving.

-Hal
 

Dansos

Member
Yeah I’ve never used sand when backfilling but we have never trenched an actual road and when we were excavating, there was very little good fill (lots of rock and ash) so I figured the sand would give us some extra insurance. I do not want to do this twice!! Lol
 

hbiss

EC, Westchester, New York NEC: 2014
Guess you don't have the animals we have here who like to stab with the shovel to distribute the sand and break up any clumps.

-Hal
 

ActionDave

Moderator
Staff member
Guess you don't have the animals we have here who like to stab with the shovel to distribute the sand and break up any clumps.

-Hal
I'm sorry you live in a world where everyone is against you, most of us don't have to deal with that.
 

infinity

Moderator
Staff member
Yeah I’ve never used sand when backfilling but we have never trenched an actual road and when we were excavating, there was very little good fill (lots of rock and ash) so I figured the sand would give us some extra insurance. I do not want to do this twice!! Lol
Around here the type of back fill and what is underneath the conduit is something that inspectors actually look at. If your pile of back fill along the side of the trench is full of rock and debris the inspector will make you use sand or some other clean fill.
 

Dansos

Member
The majority or fill is small rock but under the asphalt is a lot of red ash and coal. The size is not what bothers me as much as the sharpness of the rocks. We actually ran the piping yesterday and I had 3 yards of sand dropped off. Laid approx. 6” down and ran the pipe and then filled in on top with the rest. For $166 delivered, it seems like a very good investment. Now they can ramp down everything and I am not worried about crushing at all
 

PaulMmn

Senior Member
The problem is not so much the rocks in the fill (unless cinder-block size and larger), but the backhoe just pushing everything back in the trench, with the rocks falling down on your nice, new pipe. Plumbers did that to the line to my septic tank when they replaced it. So far, no leaks (more than 10 years out), but I cringed with every rock that dropped into the trench.
 

kwired

Electron manager
I always use sand. Not only does it help protect the pipe during backfill, but if someone is ever excavating in the area in the future, seeing the sand helps warn them of the buried utilities.

I also lay marking tape in the trench just under the surface of the top layer of sand. Aluminum-mylar foil tape has the advantage of being locatable (not much of an advantage with electrical conduit, but a big help with other utilities like water, sewer, and fiber). The tape does have a tendency to break easily if the labor is too rough installing it, so caution them not to pull it tight and to keep putting sand on it as they lay it down. Also, store it out of sunlight.


I have a lot of areas around me with sandy soil, no need to bring in other sand at those places;)

Do have areas with hard clay also though.

Natural rocks are not an issue anywhere nearby, if it is rocky the rocks were brought in at some time.
 
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