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?:o

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 :D



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

Dion got it :2tsup:

[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.

[Gingermick]

I'm not forking out another $715 for another soil test .

you already have the results so another wont be necessary.
So did the 24 100 by 100 wooden posts change to 24 300 dia posts stuck 3000 deep? Or is it just a few on the perimeter and in the middle?
And you could always talk to the engineer who designed it and tell them that you have issues with the constructibility of their work, and ask why had they not designed a raft footing. they may say that there would be too much concrete, but ask them.
You paid them to produce something you could build and they didn't, so you should know the reason why.

[ian]

The shed is 12x6.6m. Timber framed and clad, full of big heavy machines.
There are 24 posts, 100x100hwd, 500mm in ground, 400mm out.
which following the soil test has become 24 x .3 dia x 3.0m deep

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.Andrew
I've added a comment and highlighted what I think you meant by your first post.

this is what I interpret from the info provided
Your shed will be located on reactive soil it therefore needs to have a deep foundation
your engineer has specified 24 x .3 x 3m deep piers — these will need to extend 400mm out of the ground (you can't change from concrete to timber 500mm below the surface as that defeats the purpose of putting in 3m deep piers

I calculate that you will need arround 2 truck loads of concrete (about 6.5 cu.m) to pour 24 piers

An alternative design is a reinforced concrete raft that will "float" on the reactive soil


My other observation relates to your shed being "full of big heavy machines"
has the shed's suspended floor been designed for this sort of load, or have you adopted a normal domestic floor load?
You'll pretty quickly get sick of it if the floor vibrates everytime you turn the lathe on

[funkychicken]

The posts sit 500mm into the concrete, the concrete is 3mx300mm dia.

The shed has been designed to take the weight of all the machines, the Building Designers did a good job

[ian]

Understand
but I'd still be inclined to bring the concrete 400mm out of the ground and dispense with the posts, tieing the shed bearers directly to the concrete posts — gives much better protection against termites than posts burried in concrete and you don't have the hassels of plumbing the post as the concrete goes into the hole.

If you stay with concrete encased timber posts, wrap them in 6mm polystyrene foam before pouring the concrete — makes it much easier to remove at a later date if you ever have to

[Burnsy]

Ask the engineer for other options, going to 450mm or 600mm diameter should mean you can reduce the depth, it was the case when I did my house.

[funkychicken]

Ask the engineer for other options, going to 450mm or 600mm diameter should mean you can reduce the depth, it was the case when I did my house.

Would the amount of concrete needed be any less?

[Burnsy]

Would the amount of concrete needed be any less?

Could be, it is not based only on concrete mass though. If I am correct there is some coefficient they use based on concrete mass and concrete/soil surface area. Should not cost you any extra to ask the question but you may need to pay for them to print out different standard drawings.

[HazzaB]

Hey Funky,

Just ask your Ginger Beer (Engineer) if he has heard of screw piles?? these are used a lot over here in the west in the sandy soils, they are srewed in with a big excavator and they can be designed to accomodate any loading requirements, and you don't get whiteants in steel piles, and no conk required.

Just my 2 bob's worth, I hope it might help.

HazzaB

[ian]

Would the amount of concrete needed be any less?a 450mm dia pier uses 2.25 times the concrete per metre of a 300mm dia, so would need to less than 1.3 m long to "save on concrete"
at 600mm the length would need to be less than 700mm

(gee I hope I've done the maths right)

[Wooden Mechanic]

Hey Andrew, stop being a baby and dig them yourself.... :p

I would gladly come dig them, but..... :D

Take some pictures when you start! :2tsup:

Harlan

[funkychicken]

I called the engineers, they said that the current design is the best.

I called the driller man, he charges $90ex per hour and it might take 5 hours to drill the holes.

I worked out that I'd need 20m3 of concrete at $181.30cm3. $3620 in total:oo:

[snapman007]

I called the engineers, they said that the current design is the best.

I called the driller man, he charges $90ex per hour and it might take 5 hours to drill the holes.

I worked out that I'd need 20m3 of concrete at $181.30cm3. $3620 in total:oo:

Hey FC, how did you arrive at 20m3 of concrete. I get 5.1m3 based on 24 at 0.3dia x 3.0m deep. Check the quantities with the engineer.
By the way, concrete is about 1000 times cheaper on the Coast :)

[ian]

Andrew

these are my calcs

each 300mm dia, 3.4m long pier requires 0.24 cu.m of concrete
24 piers works out to 6.4 cu.m (including 10% allowance) = minimum of two trucks
(whatever you do, unless the second truck is on site don't partially fill a hole with the last of the load from the first truck)
concrete cost $1160

each pier will have a reinforcing cage in it – possibly 6 x 12mm bars plus a spiral hoop (buy the reinforcing bars pre-cut to size and tie them together, don't weld it) and make sure it's centred in the hole
each pier will probably be cased in a carboard tube or metal – at least for the last metre or so – cut the tubes at the "right" height and you have instant leveled stumps – so include a tie down in the reinforcing.

you'll need a reliable concrete vibrator, or two, and at least one helper

and you'll want to have a bobcat on site when you drill the holes to move the dirt out of the way

[funkychicken]

I got my radius confused with my diameter, thanks for clearing that up (and saving me $3000)

Who should I see about the cages and tubes and such?

[ian]

Andrew

to save me looking it up, where are you located in relation to a major centre?

what is the design for the piers?
can you scan / photo the plans and post here?

[funkychicken]

I'm about 20kms from Toowoomba, what should I look under in the yellow pages?

[ian]

I'm about 20kms from Toowoomba, what should I look under in the yellow pages?I just Googled
reinforcing steel Toowoomba
and got about three hits

what you should look for depends on what you intend building and that should be shown on your plans.

are your piers reinforced?
if so what is the specified reinforcing?
How are the timber stumps attached to the piers?
what tie downs do you need?

From what you've described here and elsewhere sounds pretty straight forward once you get 400mm off the ground.
Getting there from 3000mm below the surface could be the tricky bit.

I must admit I don't like the idea of stopping the concrete and starting the timber stumps 500mm below the natural surface — to me it sounds too much like a dinner invitation to the termites plus potential problems from the reactive soil backfilled against the timber stumps.
Can you elaborate?

[Greggy1]

We've just had to put in a similar foundation for our house. 48 of the b*ggers all 300mm diam and between 2.5m and 3.5m down.

Excavator or bobcat with earth auger is the answer. As the augur goes deeper, they undo the drive shaft and attach an extension and keep going.

Assuming you have to put re-bar down the hole as well. What our builder did was wire up the assemblies and had the concrete truck onsite. Excavator comes through, bores the hole, apprentice drops the reo in and holds it while concrete truck follows and fills it, 10mins per hole thanks for coming. I think 3 days and the whole job was complete

What that did was saved cost on cardboard or steel columns to stop collapses and meant the site was much safer as there were no holes at the end of each day.

Edge beams, waffle and slab followed, which raised us 200mm out of the ground, but probably more than you need to do by the sounds of it. I'd suggest approaching it like we did but maybe leaving the concrete 500mm from the top and dropping in your (presumably) concrete stumps inside the reo and pouring the rest the next day.

[ian]

I'd suggest approaching it like we did but maybe leaving the concrete 500mm from the top and dropping in your (presumably) concrete stumps inside the reo and pouring the rest the next day.This is not a good idea as it induces a hinge and largely defeats the purpose of digging the 3m deep hole in the first place.

[funkychicken]

One detail on the plans says "4/N12 Bars. 75 Cover."

I'll take a piccy of the plans tomorrow.

The post go into the concrete, the concrete surrounds the posts

[Gingermick]

what about ligs? 4/N12 bars need to be tied together to go in a hole.

[funkychicken]

Ligs? There's an added note, "R6 Ties at 600crs Only if required to maintain specified coverage and spacing of bars"

[Gingermick]

that'll be them. It may be hard to keep separation and cover on the bars three metres down a little hole.

[Grumpy John]

How's the foundations coming along FC?

[funkychicken]

Well I've been thinking (or more correctly, my parents have been insisting) that instead of building a shed here I could buy a cheap bit of land (Unofficially subdivide a mates block) and stick it there, then put a house next to it.

So no holes in the ground yet. If I can't get a cheap bit of land then the shed will go here in Meringandan

[ian]

Well I've been thinking (or more correctly, my parents have been insisting) that instead of building a shed here I could buy a cheap bit of land (Unofficially subdivide a mates block) and stick it there, then put a house next to it.

So no holes in the ground yet. If I can't get a cheap bit of land then the shed will go here in Meringandanbe very careful, and pay for very good advice, if you really intend going down that path
because if you do "officially" every thing you build will belong to your mate