Electrical Trenching

[tractchores]

I haven't posted on this in a while and thought I'd provide a quick update - especially if other folks think about similar projects. In the last few weeks there has been less digging and more loader work. My town uses the NEC rules for electrical code and for this job specifically table 300.5 governs the burial depth, conduit etc. The electrical inspector requires 3 different visits - Raw trench, trench with bedding and conduit and finally trench backfilled 12" with shading material and a warning ribbon run.

In my case I backfilled with around 10 yards of sand for the first run to create about 6" of bedding depth in the entire trench length. I then installed 3 conduit runs, 2 x 1" and 1 x 3/4". Code dictates that low voltage control wires (a phone cable and video cable in this case) be separate from the high voltage (120v) lines (2 in this case). The third is a spare. The conduit had to be schedule 40 PVC and in my case code required a cover depth of at least 12" (120v GFCI), but deeper is better. In my case the depth ranged from 30" to 18". As a trick to lay the conduit I built 20' sections in the garage and then covered the ends with socks and elastics to avoid getting a rock in it. We will pull 10 gauge wire for the electric to deal with voltage drop.

The conduit then needed to be shaded with 12" of sand (about 15 yards) and then marked with warning tape. Based on the huge number of rocks it was recommended that the trench be mostly back filled with sand to avoid issues, so another ~15 yards got it mostly filled. It's worth noting that the B2920 worked perfectly for the backfill, I was able to climb the spoils pile and get enough reach with the FEL to backfill over the pile VS trying to move it around or need access to both sides of the trench. I then pushed back the excavated soil into the trench minus rocks any bigger than about 6" across (per code). The interesting this was that even with the 40 yards of sand I still had low places because of the number of rocks I took out!

The next part of the project is the actual installation of the gate and low voltage control lines and a bore under the driveway to get power and control lines to the opposite side. Then everything can be wired up.

Here are some pictures of the trench work:

Conduit on sand bedding

Conduit on bedding, it curved nicely on the uphill portion and had more flex than I expected.

Shaded with 12" of sand and flagged with warning tape

 

[arlen4720]

That looks good! I'm glad you are installing it in accordance with the NEC. Remember you have to be schedule 80 where you emerge from the ground.

 

[deathtoblackberries]

Good job but how do you get your tractor down that trench of boulders?

 

[ericher69]

Wow!

I do not own a bh65 for the 2920 but after seeing your work makes me feel a whole lot more confidant in its capabilities!

 

[SPIKER]

Just something quick, maybe run two 120vac lines out (240 between the hots) if they will let you get away with it. be sure to run some pull tape/rope in there with the wires as a leave in for later. best to pull it WITH the wires so they do not twist around each other. Seen pull tape cut thru wires that the tape had been twisted around.

Mark

 

[tractchores]

Good job but how do you get your tractor down that trench of boulders?

I backfilled from the side. I put the biggest rocks on one side of the trench, where they'll stay (I'm now moving them into piles for some future project). The other side of the trench closest to the drive had the dirt piles. The B2920 had enough clearance for me to drive up on the dirt piles and then dump the bucket into the trench. It worked out well because 1 bucket is about equal to 6' of trench filled with sand to 12". I just went bucket length by bucket length down it, then leveled with a rake and packed it down. The final backfill was done using the FEL to push the dirt into the trench and the weight of the machine to pack it. For the few areas with dirt piles on the far side of the trench I drove into the trench (front wheels hanging on edge), then lifted the front out with the FEL and back dragged the pile into the trench. It worked out much easier than expected. Now if I could just find someone to buy my rocks by the pound!

 

[tractchores]

Quick update - The trenching is done for the gate control system and electric. I dug in an exit and entry trench to 3 - 4' deep so that I could attempt to bore under the driveway. I first attempted it myself using some techniques I read about on-line. I tried to hammer a pipe through (3/4" steel) and not surprisingly - Hit a rock! I bent the pipe with the BH trying to push it through. I tried with a piece of rebar and had the same result. I tried using water pressure via a PVC wand and high pressure nozzle, that got me a few feet, but ultimately I hit a rock.

Out of desperation I started to look into outsourcing the job. A cut in the driveway wasn't desirable (new driveway) and was expensive, plus the contractors are all to busy to hit my time-frame. I then checked into directional boring (a horizontal drill basically) and the setup alone was $2,000. I finally found an irrigation contractor with a pneumatic piercing device who was between jobs. For $250 he came this morning and was able to use the device to get through at 3' deep and put 2" HPDE pipe in. The device was very cool, it uses air pressure to propel a conical metal device that's like a self propelled jackhammer through the hole and works by compressing the soil and pushing or hopefully cracking small rocks.

I'll post some pics later, but it looks like the job is getting to the final stages!

 

[k0ua]

The device was very cool, it uses air pressure to propel a conical metal device that's like a self propelled jackhammer through the hole and works by compressing the soil and pushing or hopefully cracking small rocks.

Pneuma-gopher is what they call them around here. Short for Pneumatic- Gopher.

 

[hr3]

The device was very cool, it uses air pressure to propel a conical metal device that's like a self propelled jackhammer through the hole and works by compressing the soil and pushing or hopefully cracking small rocks

Would love to see pictures of that,, I'm going to have to Google that one,,, :thumbsup:

 

[tractchores]

Here is a link to the brochure for the actual tool. http://www.hammerheadtrenchless.com...nguageId=a37c4322-49d1-4151-a78c-6a6b9f17f0fd

It was tough to find someone with it, but one of the drillers was nice enough to give me suggestions and said to try calling the local ditch witch as they rent the tools. When I talked to them it turned out training was required and the rental was expensive, but they gave me names of contractors who purchased the tools that were local and they were able to recommend a couple companies. Very cool tools, but apparently they can be tough to control over long distances and if you lose it you're out big $$. Rental looks to run a few hundred per day...