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Come on, someone on here must be an expert in CFA piles, surely?
My question is regarding the cage and how long it should be. I would only make it long enough to engage sufficient skin friction to resist any uplift, but the older generation want to put it all the way down. difference is 10m of cage (from 7m to resist uplift to 17m to go to the bottom) over 300 piles which is a lot of reinforcement.
Been years since I've carried out any pile design, but: you mention uplift case, what magnitude are the bearing loads?
The piles can fail due to compressive fracture at the base and the rebar provides the tensile strength circumferential to the pile in the lower portion.
not my field but for 3000 m of reinforcement i'd pay for a second opinion
I am the second opinion! but I don't have anything to back up my comments on the original design which I say is OK, just the person I am checking it for wants the long cages
Kevj these are 450mm dia taking 400kN so not very heavily loaded
[i]I am the second opinion[/i]
"In my opinion (and a large number of underqualified, underinformed or both mtbers I consulted agree with me on this)..."
Hi, I was a designer at a piling contractor for a number of years, now in consultancy, drop me an email if you like - details in profile.
Wwaswas, get back to your shipping forecast!!
How confident are you in the soils information you are working with / ground model and that in all cases sufficient skin friction will be mobilised from the upper section of the pile ?
I frequently deal with piles.
What's the question again?
DrP
Tim got your email, will respond in a bit (waiting for the bus home!). Will try and keep any comments regarding structural engineers trying to understand geotechnics private 😉
It'll be fine, just fill any voids or cracks with expanding foam.
I fix telephones for a living(badly, if today's efforts are anything to go by)
I would avoid designing full length cages for CFA piles as you would probably struggle to install 17m long cages. We would typically keep the cages less than 12m and install a central bar (if required) to deal with any tension.
DrP
It comes down to whether I can pull really hard on a pile or is that a bad idea?
^^^ if you're pulling more than pushing then it's a ground anchor 🙂
[i]install a central bar (if required) to deal with any tension. [/i]
"Did you spill my pint?"
"Sorry mate, here's a tenner go and buy another at the central bar over there."
"Cheers, thanks"
Just emailed you my thoughts, basically 8.3m assuming a cu of 70 in the clay. Forgot to add, but really you should also check bond capacity of the rebar to the concrete as well. Also, depending on the addition length this adds to your bending requirements, you could consider just using a central bar for tension.
^^^^
Yeah, this. 8.3ish should do the trick. Double check bond capacity though - I know you slack on that.
DrP
Thanks all!!
Welcome.
DrP