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Deck supports

| Posted in General Discussion on July 30, 2000 10:09am

*
I’m wondering if I’m going to have trouble with the Sono-tubes (spl?) my excavator put in.

Though placed on virgin soil and below frost line, I’m certain he didn’t pour a footing for the tube to sit on. Every description I’ve read to date about how to install the tubes says to hold them above the bottom of the hole and let the concrete ooze out to form a footing.

It’s been over a year and they haven’t moved, but there’s no weight on them either.

If trouble is in the offing, would pouring a grade beam between them help?

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  1. Guest_ | Jul 30, 2000 06:14pm | #1

    *
    b TVMDC

    What you have is a friction pile which resists sinking from the skin friction between the cement and the soil. You can have a soils engineer calculate the total allowable loading for each pile based on the total skin surface (2 x pi x radius x depth-of-pile) x soil resistance per sq foot. It may cost you a couple bucks since the engineer will have to take core samples of the soil and test them in his lab.

    1. Guest_ | Jul 30, 2000 06:45pm | #2

      *sorry bill.. i think he's got bearing piles....they were sono-tubes placed by his excavator.they weren't driven.... so there was no friction developed.. their only bearing capacity is that developed from the soil in contact with the foot of the tube (i.e. 8 inch tube = apx. 1/3 sf., 12inch tube = apx. 0.8 sf.) Here in RI , CABO one & Two Family Dwelling code: table 401.4.1 lists bearing capacity of sandy gravel at 5000 psf, and silty clay at 2000 psf.flash... picking up the sono-tube only increases the bearing area... if the bearing area of your tube is sufficient for the bearing capacity of your soil.. and the load that is going to be imposed on them.. then everything is hunky-dory..if either one is deficient then the grade beam may not correct anything...first , the bottom of the grade beam will also have to be below the frost linesecond the attachment of the grade beam to the sono-tubes is a problem..your state building code makes certain suppositions..one is the minimum bearing capacity of your soil..using this you can calculate the bearing capacity of each sono-tube post.. if they are not sufficient you have two choices.. either hire a soils engineer to do as-built bearing capcity with core samples from the depth of the bottom of the tubes ((Soil Test))or pull the tubes and replace them with ones that have a footing with bearing capacity you need...the short answer is... they are probably all right... IF indeed they were poured on virgin, undisturbed, suitable soil (not peat, or clay) , below frost line.....b but hey, whadda i no ?

      1. Guest_ | Jul 30, 2000 08:41pm | #3

        *b TVMDCI sit corrected!

  2. flash | Jul 30, 2000 10:09pm | #4

    *
    Thank you gentlemen!

    They are 12" tubes and my thinking was " how much does a 6X6 have to sit on ?"
    Had I elected to continue the 6X's to below frost line I don't think I personally would have put them on much more than that anyway.
    But, then, I've seen those plastic funnel shaped devices to attach to the tube and, without total confidence in the excavator, thought I'd better ask.

    I swear John Deere must have put a "tree seeking"
    navigational device in their 450's.
    Guy didn't miss a one!

  3. flash | Jul 30, 2000 10:09pm | #5

    *
    I'm wondering if I'm going to have trouble with the Sono-tubes (spl?) my excavator put in.

    Though placed on virgin soil and below frost line, I'm certain he didn't pour a footing for the tube to sit on. Every description I've read to date about how to install the tubes says to hold them above the bottom of the hole and let the concrete ooze out to form a footing.

    It's been over a year and they haven't moved, but there's no weight on them either.

    If trouble is in the offing, would pouring a grade beam between them help?

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