How to dig the narrowest 3' deep trench or minimize sand fill for a wide trench?

[TORQUIN]

If renting a trencher from Home Depot, verify that it will go deep enough first, then test it as soon as you get home. I rented one from Home Depot back in 2016, that was supposed to be able to trench to 28", for my gen set wiring. In reality, it was unable to get to that depth. I had to finish the job with my back hoe. Home Depot gave me a refund on the rental since the equipment could not do the job.

Chris

 

[bgr]

As a fellow new englander, I am sure you will see a few big rocks, and also a lot of small and medium ones mixed in your backfill soil. Sand is your friend because you can backfill it by machine. If you use your backfill, you will have to do it by hand for the first 12 inches because you will want to sort out the rocks from the soil going onto the conduit. That is a lot of work. Use the 12 inch bucket to trench.

My electrical inspector would want to see the trench with 2 inches of sand under the conduit and 12 inches on top, plus the caution tape laid directly above the conduit on top of the backfill sand. He would want to see some parts of the trench completely backfilled with the tape in place and every 30 feet or so, backfill left out to show the conduit. If you have an inspection, I would ask the inspector what he wants to see before you start. Be sure to use caution tape with a metallic element so the trench can be found with a locater.

I think the idea of having the fiber people pull in their line after you finish the trench is a good one. You would have to be sure one side of the trench backfill was smooth and rock free to accommodate their trenching or pulling machine after you were done. or you could lay the fiber on top of the sand backfill on the opposite side of the trench from the conduit, AFTER your inspection is complete. My inspector always wants the visible sections of conduit to have the maker's logo on top and visible where the conduit is exposed.

The sand required would be 1.2(foot) x 1(foot) x 300(Feet) = 360 cubic feet. divided by 27(cu. ft. in a yard) = 13.3 yards. I would get 20 yards, or whatever your supplier's truckload is, as you can always use a little extra in case the trench is not a perfect 12 x 12 shape in some spots and it is faster not to carefully ration it.

You are going to need a teenager to help spread the sand evenly as you drop it in if you can find someone. I have found it quicker to do the 2 inch base of sand in the whole trench, go back and glue the conduit out of the trench, roll it in in one piece for the whole trench, then go back and put in the 12 inches of sand. That puts less strain on the fresh glue joints, and makes sure the conduit is clean, with no sand in it. Be sure to tape the ends closed before rolling it in. Tap the conduit sections together with a light sledge and a wood block over the ends as you glue it. The joints on 20 foot sections are deep and you want to be all the way in for strength But you will find your own system. Always look down each piece of conduit for no obstructions before you glue it.

My instructions are detailed because every detail comes from a screw up. Hope your job goes well.

 

[orezok]

Being a licensed General Contractor for 35 years, I would NEVER stack high voltage, low voltage lines vertically. Thats a future NIGHTMARE!

 

[thclimer]

Prior to where I now live I lived in NY near the Canadian boarder, north of Plattsburgh. In that area I would dig a hole or a trench which would consist of 30-50% rock. Anywhere from baseball to bathtub sized, just crazy. Good luck keeping your lawn free of rocks as each year the frost would push new ones to the surface.

 

[John_Mc]

Not sure where you are located, but in my area, sand is cheap. Just as a rough calculation: let’s say you need a total depth 16” of sand (to get some under and the 12” over, and your trench is 17” wide and 300’ long. That’s about 21 yards.

Even if I’m off and you need to go 20”x17”, that’s 26 yards. A full load in runs about 13 or 14 yards in the dump trucks our town road crew use (which are the same thing most gravel and sand suppliers in our area use.) I’d just get two loads of sand delivered and dig the trench with an excavator. (I’ve run walk behind trenchers and they are a pain in the butt here in Vermont’s rocky soil.)

 

[Gord Baker]

Ok. I am deferring to the power of group think here. Here is my situation. I need to trench 300' for electrical and telecommunication conduit. Electrical is 3" wide conduit and telecommunication will be 2" conduit. The minimum depth for electrical is 30". I am trenching from a pole that is pretty much in the drainage ditch next to the road and up a hill. I am guessing I'll start somewhere around 36" at the pole and be around 3-5' deep when I start ascending the hill. Over a certain number of feet I'll eventually get back up to the 30" (36" to be safe). I think I got that all worked out. Here is my issue. The electrical service is asking for a bed of sand(or stone dust) below the conduit and 12" above. I can't get any answer out of the fiber internet company so I was going to do the same for their conduit. No problem but here is the issue. The telecommunication conduit needs to be 12" away from the electrical. If I dig a wide trench to accommodate both conduits and the spacing, I am looking at a minimum 17" wide trench. Realistically it'll probably be closer to 20". Ok. So what is the problem? The problem is the 12" of sand on top of the conduit. How do I get 12" on top of both conduit and not have to buy a ton of extra fill for the 12" gap in between? I had considered renting a trencher but that might be a little treacherous on the slope and I would need to put a much large gap in the rock wall to navigate through. Plus, being in New England, I'll likely hit some large rocks. Then what? It's not like you can just bend 3" around them or dig multiple new trenches hoping to find a clear path. There is also the fact the electric company only allow a certain amount of bend in the run and I already need to do a 45 degree turn at one point.

A trencher, that can go that deep, is about $310/day from Home Depot. I'd have to do some serious looking to find one somewhat local for cheaper. The easy route is just do the wide trench with the CAT 306 but the cost of filling that 12x12x300 area, in between conduits, is prohibitive.

I recommend getting it professionally done. 2 trenches. 36"+ deep. Carefully Map out where they run. In Ontario a Red Marker tape is required a foot above the conduit. A good idea even if not required by Code.
You might also ask your phone company if they have a contractor that would Bore it Out. 3" seems too big for a simple power and/or communications conduit.