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After reading most of the posts from folks who have contracted, or DIY ground mount arrays with trenched cable/conduit runs, I am left with the impression that power augers are not much use in rocky soil. After quite a bit of searching, I found a gas powered digger used mainly by orchard managers, that could be adapted to digging post holes & trenchers, but is not ( apparently ) available for rent in Southern California. Several local rental outfits do, however rent gas-powered breakers, primarily used for pavement breaking, but are available with a spade-type end, instead of the usual pointed gad-bit. They rent, typically for $80/day, and weight about 55#, which is a pretty good "handful", even for a large young guy ( of which I am neither ). The landscaper's Dyna-Diggr is commonly available in Florida, and weighs about 40#. If I go the gas breaker route, to speed up the earthwork part of the project, I would hire a couple of HD day-laborers to do the work ( trading off on the breaker, shovel & manual post-hole digger ). Like most on the Forum, I am most eager to hear from any of the folks who have first-hand experience with these tools, either as DIY, or by observing their installers. Any takers, please?
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I'd probably look at renting a post-hole auger attachment for a bob-cat(skid-steer) and the skidder to put it on.
Or something similar.
I think that'll work for anything that would work with a spade bit on a demo-hammer.
And while I haven't used one, it looks a lot easier to use than a 1-person or 2-person hand-held setup. (And looks a lot faster per hole)
If you have BIG rocks, then maybe you have to plan on a jackhammer/demohammer.
"rocky soil" can mean a lot of things - it can mean a bunch of 3/4" and smaller gravel, which an auger would handle.
Or it can mean large rocks that a person can't lift. -
We have rocky gravel soil. 4 beefy people on a 2 man auger will still break hips when it hits a rock. We found a small tow-behind auger at a rental place, on 2 small wheels, and just takes 2 people to roll it around and it digs down in just a couple minutes, same hole the 4 person auger took 30 minutes for.
There are also augers for skid steer/bobcat that would make quick work.
Trenches - found hitting a good size rock would throw the belt off a Ditch Witch, and spend 40 min taking it apart and back together, a mini-excavator on treads was much faster.Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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On some areas I have a great density of rocks, though they are pretty much small
enough to lift easily with 2 hands. Post hole diggers are marginally successful. It
seems like digging a trench with a back hoe works better. Bruce RoeComment
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Up in New Hampshire where the soil is mostly rock with soil mixed in between the cracks, the only option is a backhoe or crawler loader. Many contractors have tried trenchers and most have given up quickly.Comment
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Don't reinvent the wheel. Your local rental place can tell you what works in your location for the depths you need. How deep are the footings?
In socal you should be able to find a trenching subcontractor.Comment
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Bean and Rice powered digging tools are cheaper and more reliable in rocky conditions.... than gas.Comment
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With reference to an earlier post, I noted that my conglomerate soil is evenly graded, from silt up to 15" rocks. With the emphasis on "evenly", percentage of soil "particles" of a specific sieve-size is pretty much inversely proportional to size. Over 50% of my test sample had particles < 1/2" in diameter. Of the remaining 50%, half were < 1" & so-forth. With eight 16"x42" pier holes, as proposed, I would expect to find 6-8 8" rocks that needed to be pulled out by hand, but enough 4-6" ones to predictably freeze a 5.5HP gas auger several times, in the course of digging eight holes. Over the last year I explored both the possibility of renting suitable ride-on trenchers & medium duty towable power augers, & subcontracting out the whole shebang. At that time, all the local reputable landscape contractors were booked solid, but the situation may have changed, so that option is still on the table. Subcontract earthwork has the advantage of putting the Workers Comp monkey on their back, instead of mine. A towable power auger seems viable, as I can winch it down 60' from the road above, down to the level array site. On the other hand, there is no way I am going to put an inexperienced bozo behind a walk-behind wheeled trencher or Bobcat, on my 27* crumbly hillside ( my homeowner's insurance is high-enough already ). Tracked rental trenchers are hard to find in my area, & very expensive.Comment
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