Digging a 3000mm deep hole

[funkychicken]

I just received the stump design for my shed ($715) and it specifies that the post holes need to be 300mm dia x 3000mm deep. What exactly drills holes that deep?

[Big Shed]

Are you building on a swamp?

You need a pile driver.

[funkychicken]

The spot where the shed's going is supposed to be a filled in floodplain, and we're on gosh awful black soil

[watson]

G'day Funky,
It might be time to step back from this project a little bit and look at it with some cold hard logic.
Think about the house.......does it have 300mm x 3000mm stumps???
I don't think so.
So maybe what you're asking people to assess or design is somewhat askance.
Just a thought.

[Dion N]

I just received the stump design for my shed ($715) and it specifies that the post holes need to be 300mm dia x 3000mm deep. What exactly drills holes that deep?

Excavator with earth auger attachment - check with your local earthmoving guys

[funkychicken]

The house is on a different part of the property, it's on solid rock. In some spots they could only drill down 600mm before hitting rock

[echnidna]

A shovel with a realllyyy long handle

Excavator with earth auger attachment - check with your local earthmoving guys

Dion got it

[ian]

What Dion said or a truck mounted earth auger

and at 3m deep you'll almost certainly need to case the holes as they are drilled (= additional expense), and pouring concrete into them making sure there are no voids is not a simple task

1) can you move the shed somewhere else on the property?

2) given you're on black soil or flood plain fill, a reinforced raft may be a better option, allowing you to do much more of the construction labour yourself — ask your designer

[.RC.]

Sounds like overkill to me, how big is the shed???

[artme]

Ian is on the right right track Andrew. If you already have council approval for the shed and its siting It may cost a few dollars for a variation to the approval bu that may well be less expensive than the cost of the holes at 3000mm and the extra length required for the poles/posts.

[Gingermick]

I dont know how a designer would react to being told his design is unworkable for you. They'd want a variation.
How big's you shed? Is it four storeys?
They must work for one of our rivals.

[VernJ]

My Bro lives in Dirranbandi. He has told me about what has to happen out there to stop a house from falling off it's stumps. All very complex and deliberate. Deep auger holes that are then undercut at depth, special cardboard liners, etc etc etc. Otherwise the stumps just wander around the place ... I'd suggest that it's worth getting it right, first time round ... stumps in reactive soils can move heaps in just one season.
Good luck!

[AlexS]

Ah, the black soil country. Stick to it in the dry, and it'll stick to you in the wet.

[funkychicken]

The shed is 12x6.6m. Timber framed and clad, full of big heavy machines.
There are 24 posts, 100x100hwd, 500mm in ground, 400mm out.

I can't relocate the shed, there's no other space for it and I'm not forking out another $715 for another soil test and stump design and getting the plans adjusted again.

[echnidna]

Driving piles is probably the easiest and cheapest way.