CFA Piling

  • This topic has 19 replies, 10 voices, and was last updated 3 years ago by  DrP.
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  • CFA Piling
  • Premier Icon TimP
    Subscriber

    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.

    kevj
    Member

    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.

    T1000
    Member

    not my field but for 3000 m of reinforcement i’d pay for a second opinion

    Premier Icon TimP
    Subscriber

    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

    Premier Icon TimP
    Subscriber

    Kevj these are 450mm dia taking 400kN so not very heavily loaded

    Premier Icon wwaswas
    Subscriber

    I am the second opinion

    “In my opinion (and a large number of underqualified, underinformed or both mtbers I consulted agree with me on this)…”

    Premier Icon honeybadgerx
    Subscriber

    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.

    Premier Icon TimP
    Subscriber

    Wwaswas, get back to your shipping forecast!!

    marcus
    Member

    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 ?

    DrP
    Member

    I frequently deal with piles.
    What’s the question again?

    DrP

    Premier Icon honeybadgerx
    Subscriber

    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)

    RickyRah
    Member

    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.

    Premier Icon TimP
    Subscriber

    DrP

    It comes down to whether I can pull really hard on a pile or is that a bad idea?

    Premier Icon iainc
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    ^^^ if you’re pulling more than pushing then it’s a ground anchor 🙂

    Premier Icon wwaswas
    Subscriber

    install a central bar (if required) to deal with any tension.

    “Did you spill my pint?”

    “Sorry mate, here’s a tenner go and buy another at the central bar over there.”

    “Cheers, thanks”

    Premier Icon honeybadgerx
    Subscriber

    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.

    DrP
    Member

    ^^^^
    Yeah, this. 8.3ish should do the trick. Double check bond capacity though – I know you slack on that.

    DrP

    Premier Icon TimP
    Subscriber

    Thanks all!!

    DrP
    Member

    Welcome.

    DrP

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