Need to dig a trench

Discussion in 'Horn Depot' started by wherzwaldo, Mar 16, 2011.

  1. wherzwaldo

    wherzwaldo 1,000+ Posts

    My employer (in Austin) needs a ~1200' trench about 18" deep to bury a 12-strand fiber optic cable. Electrical/water/irrigation lines would need to be avoided.

    Any advice on who could do the dig and backfill, and possibly even lay the cable, for a decent price? One company gave us a quote of $10k just for the trenching but that seems high. Is this a day labor type of deal or should it be left to a professional (my boss would probably prefer the latter)?
  2. eugene11

    eugene11 250+ Posts

    contact your local army surplus store for dynamite since you are trying to do this hear in central texas. [​IMG]

    sorry i dont have first hand experience with anyone here except my self and it was a ***** just to go 6".
  3. brntorng

    brntorng 2,500+ Posts

    Don't have experience with any specific company, but this is one of those jobs that needs to be done right due to the potential liability if something like a gas line was severed. Every utility supplier has to mark underground cables, pipes, etc. that are in the path. In Austin, there is one number you can call to have all the utilities send out someone to mark their underground facilities. It takes a week or two for this to happen before you can start to dig. Also, there are standards for how deep certain things need to be buried. For fiber, I suspect it's not very deep since there's no safety issue. It's more a matter of it not getting damaged. Due to the rock that exists under much of Austin, this is also a job for someone with heavy equipment. BTW, I presume you're going to bury conduit to protect the fiber and so you can pull whatever you may need in the future.
  4. wherzwaldo

    wherzwaldo 1,000+ Posts

    We were trying to decide between pulling it through a conduit or just laying armored cable and throwing dirt on top of it. This is also why we wanted a professional consultation, to tell us whether our ideas were stupid or not.
  5. BigWill

    BigWill 2,500+ Posts

    if you just use cable, the trench will need to be "shaded"...that is, you dig the trench, lay a bed of sand, place the cable, and lay a bed of sand on top of that, and finally replace the native material.

    Go with conduit. It's cheaper.
  6. Uninformed

    Uninformed 5,000+ Posts

  7. l00p

    l00p 10,000+ Posts

    You still got the gas company out to make any markings if need be, right? What kind of turnaround from call to visit do they generally provide?

    you may want to call ahead to make an appointment with the Gas Co. I don't know if there are other digging considerations in your area or not but check just in case. (obviously)
  8. wherzwaldo

    wherzwaldo 1,000+ Posts

    This would be in NW Austin, Mopac/Braker area.

    I found the number to call for all the utilities to come do their markings. We generally already know where all of the utilities run, though; we are mostly concerned about irrigation and private electrical lines on the property.
  9. YoLaDu

    YoLaDu Guest

    1200 feet. That is quite a distance. Could that scope of work possibly require a site development permit? Are there any easements or has that been ascertained?
  10. wherzwaldo

    wherzwaldo 1,000+ Posts

    It's all comfortably on private property, but you may be right about the permit.
  11. nashhorn

    nashhorn 5,000+ Posts

    Wow 1200 feet is definitely a long run. I thought Aluminum wire was outlawed for elect purposes? Is that just for in-house application?
  12. BigWill

    BigWill 2,500+ Posts

    yes, aluminum is no longer used in houses.
  13. Uninformed

    Uninformed 5,000+ Posts

    The aluminum wire that I am talking about was permitted last year and was inspected - I don't personally know the codes but my electrician and electrical inspector sure the heck did. There is a cable running from one box in the garage to a second box on the opposite side of the house through the attic (I don't remember the wire we used for that run). There is a short run from that fuse box to a pool specific box and then there is a 75ft. run of aluminum through conduit terminating in a Jandy Aqualink control box to control colored lights, heat pump pool heater, waterfall, a few pool pumps and landscape lighting. BTW that control box is great as everything can be controlled remotely from a handheld device.
  14. wherzwaldo

    wherzwaldo 1,000+ Posts

    My parents' house has aluminum wiring, and whenever my dad replaces a switch or fixture he always uses this goop that keeps the wire from oxidizing. However, the aluminum wiring has caused one fire in the house and almost caused another one. I would be curious to know why the electrician chose aluminum over copper.
  15. BigWill

    BigWill 2,500+ Posts

    yeah, alum is still used for "main" runs, as it's cheaper than copper. It isnt used for outlets and switches though.
  16. ghost

    ghost 500+ Posts

    Get the utility locates done first, which includes probing the water line. I would go with a reputable GC although I don't know that they would take on such a small job. Call some local construction companies and see what they say.
  17. Uninformed

    Uninformed 5,000+ Posts

  18. Thunderhoof

    Thunderhoof 250+ Posts

    Aluminum has more resistance than copper. More resistance = more resistance, thus more heat. This constant heating and cooling can cause it to loosen in its lugs and other connections, which can lead to arcing and fires. Most of the aluminum I have seen is large, stranded wire these days. Granted I'm no electrician.

    On the trench, it really depends if you have soil or rock. Seems like where you are talking about there might be some soil there, in which case a trencher would work fine. If it's rock, you will need to rent a saw instead. They are typically more expensive, and I seem to recall spending ~$300/day on a rental.

    18" is a safe depth, because electrical also has to be a minimum of 18". The conduit advice above is good advice. If your employer has the money, you should run more conduit than is required for the fiber. Conduit is cheap, but re-digging a trench is not. If you lay more than one run in the bottom of the trench you will always have the ability to pull more stuff through there later if you need to.

    Also, if you are in rock it is a good idea to surround the conduit with sand anyway. Tree roots pushing the conduit into sharp rocks over time can and will break it.

    Furthermore, consider how straight the trench will be. If you make enough twists and turns, it will be impossible to pull anything through the conduit. Try to keep the total degrees of the conduit bends under 360 degrees (4 90 degree bends, for example). You may need to add some pull boxes to the run if you cannot do that.

    But really consider the extra conduit. Believe me, if there is any chance in hell that you will need it one day, you will be very happy that you did it.

    On that 10K bid, I suspect that fiber was a significant part of the materials portion of the bid. It is pricey stuff.
  19. wherzwaldo

    wherzwaldo 1,000+ Posts

    The $10k bid was just the trench, no fiber, no conduit. And fiber is not that expensive, we were expecting to pay $1-2/ft.
  20. zzzz

    zzzz 2,500+ Posts


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