Digging a 3000mm deep hole

[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....

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

Take some pictures when you start!

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

[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

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?