Collapse pressure of steel casing 1

[MarioGr]

Probably have been done to death here but after reading numerous threads and googling the hell out of it and consulting Roarks I am none the wiser so here I am.

I have a drilling client working out woop woop in Australia. (It's near 'Out to Buggery'.) They will dig a hole some 2.0m x 2.0m and drop a 1800mm diameter casing that is 1200mm deep with an 8mm wall into that hole. They will then backfill and compact against the casing on all sides. (Possibly using a high slump mass concrete mix which is neither here nor there.)

Here's the important bit. They will then place a drilling sub-base immediately adjacent the hole/casing. That sub-base when fully loaded with the drill rig in position will exert a surcharge loading to the soil under of 130kPa.

With a soil friction angle (Ka) of 0.33 I get a lateral pressure to the casing of 43.3kPa due to the surcharge.

Ignoring the soil conditions, whether it was compacted evenly around the circumference , whether the subbase is exerting a UDL is there a formula that you can calculate to work out either the required thickness of the wall required or the collapse load of the casing?

The Roarks formula I have seen here posted previously is for long thin walled tubes. The D/t ratio for this casing exceeds the parameters of the formula they use.

Do I just calculate the hoop stress or is it more involved?

Would someone be kind enough to help? Thanks in advance. (Red arrow points to casing. Floor grating over half of casing.)

 

[FacEngrPE]

I suggest if you are unsure you can get reasonable compaction around your cylinder, consider using flow fill, or a cement slurry using local soil in place of sand on the outside of the cylinder. Mix to the consistency of a milk shake, the cement mostly makes the mix runny. A result with a cylinder break test of anywhere between 500 and 1500 psi should provide reasonable support.

 

[MarioGr]

@1503-44, @SSCon. Thank you.

And thanks to everyone else too. Appreciate your input. Great reading. Learnt a lot.

Had to laugh though I sent them an email Friday to say it's going to be OK only for the bloke on the other end tell me there's going to be a delay for the steel ones and can they use an 1800 diameter by 1200 deep concrete pipe!? You have to laugh. So come Monday I'll be trying to chase down the manufacturer of the concrete pipe. Presumably if I can find who made it they will have load tables for this as that's what they're used for all the time. (Or not.)

On the plus side, 2 certifications = 2 invoices.

 

[1503-44]

Welcome. Isn't that always the way it goes.
I love all the Army EMs. They are usually have very practical solutions to the most common problems.

I'm pretty sure concrete will work.
Greater wall thickness can be more important than allowable stress.