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  1. #1
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    Default OT: Formula for figuring concrete in hole

    I need a formula for figuring how much concrete to order for a hole that is 2 feet in diameter and 3 feet deep for 18 holes. Or will take the answer.

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    9.425 Cu. Ft. per hole

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    Default yards

    how much concrete to order for a hole that is 2 feet in diameter and 3 feet deep for 18 holes
    Asuuming no posts in hole:
    r of hole = 1/2 d
    r = 1
    volume = pi*r*R*h (as explained below)
    (1*1* 3.14) area of hole x 3' x 18 = 169 cu ft
    1 cu yd = 27 cu ft
    169 cu ft / 27 = 6.3 yds total round up to 13 yds
    Hope this helps,
    Del
    Last edited by delTool; 02-24-2010 at 09:39 AM. Reason: I did circumference not area

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    How to Measure Volume of a Cylinder

    Radius=r
    pi = 3.14159 (approx.)
    Area=A
    Height=h
    Volume=v
    First calculate the area of the circle: A=pi*r*r
    Then multiply by the height to attain volume: v = A*h = pi*r*r*h

    Concrete is usually sold by cubic yards so you then convert your result to cubic yards.

    (note: Any concrete supplier company will calculate this for you so you can then compare your numbers with theirs)

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    If the void to be filled with concrete is cylindrical, the volume is (pi/4)*D*D*L, where D is the diameter and L is the length (depth of the hole). Plugging in your numbers yields 3*pi cubic feet of concrete per hole, a little less than 10 cubic feet.

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    Pi times the diameter squared divided by 4 for the area of the surface of the hole, times the depth for volume, or as RAS says 9.427 cf/hole. Subtract for the volume of a post if it's large (same formula - area of circle times depth). For 18 holes that's 169.65 rounded is 170 cf. Divide by 27 for cubic yards as that's how concrete is ordered - 6.3 yards. How good is your qc on hole diameter/depth? It doesn't take a whole lot of extra hole size to equal a lot more concrete over 18 holes. :-) Sounds like pretty much a whole truck depending on how big the trucks are out there.

    Michael

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    Here's a Calculator that lets you figure with a post in the hole.

    RAS

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    Volume = 3.142 (pi) X Radius squared X height
    9.42sf = 3.142 X 1 X 3

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    Thank you and each hole will have a 6" X 6" post in it.

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    Del was doing real well up until the round-up part where he demonstrated his background figuring taxes for the IRS.
    You have about 6.3 yards minus about 1/2 yard for the posts.

    I like to have something solid under the post like day old concrete or a large rock for vertical support and to slow down decay of the post.
    Create a good slope away from the pole.
    If you are getting a truck, a small project off to the side for the extra is also good.

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    IME, setting wood posts in concrete is a recipe for rot. We are in a drier area than you, and even hedge (osage orange) posts will rot within 10 years if set in concrete. Set in dirt, a hedge post will last over 100 years.

    I would set them in sand. Mix a little cement powder in if it makes you feel better, but unnecessary. Leave the top 6-12" for dirt.

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    Default Sand

    I don't think that I would go with sand. Just seems to me that water would drain out of surounding soil and leach into the sand filled area and set until the ground around int dried out keeping your post in water. The utility companies seem to use limerock with fines in this area. I think they set more posts than most people. Might want to ask them. .02 Rodl

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    Quote Originally Posted by KIMFAB View Post
    Del was doing real well up until the round-up part where he demonstrated his background figuring taxes for the IRS.
    You have about 6.3 yards minus about 1/2 yard for the posts.
    Ouch, I refigured cu ft, but didn't redo cuft to cu yds.

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    Here's a free calculator I wrote that calculates weight and volume of all kinds of shapes, or combinations of shapes.

    ME Weights

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    Stu, if you'll stake a 12" diameter piece of Sonotube down a few inches in each hole and up 6 or so inches above ground, then crown the concrete up toward the post for water run-off, use pressure treated posts and suspend them a minimum of 3" off of the soil, paint a thick stripe of roofing patch at the concrete/air line, they should out live you. Even after not much of the tar is visible, it will remain captured between the wood and concrete as a resilient gasket.

    When I lived in the Trinity National Forrest, an eighties-something neighbor showed me hundreds of Douglas Fir natural tree round posts he'd put in the soil 40 years before, ten foot deer fence. With pride, he asked me to guess how long they'd been in place. I guessed 5-6 years. Perfect condition.

    Having a PHD in chemistry and a Pharmacist as a living, he pointed to a 1/2" plug at the ground line of each. "Drilled 'em nearly through, filled 'em with strychnine and plugged 'em. Dry rot isn't dry and it's not rot, there must be enough moisture to support the insects and bacteria that feed on wood, you can't stop the moisture but the strychnine stops the bugs".

    Yeah yeah, the world will probably split in two tomorrow because he tucked a little natural substance in each of his posts.........a note to the faint of heart hand wringers, he didn't import the stuff from Alpha Centari, it occurs naturally by the ton right here on our Blue planet and still in the weather for 40 years, enough has remained unleached to keep the pests at bay.

    Now the old buzzard was full of it in one respect, didn't eat meat but one silly thing don't make you a sissy.... never could figure out how he could out climb 40-something me up those mountains....really pissed me off....ate more meat....30 years later, still do.....hasn't helped, yet....but he's passed on....see?

    Bob

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    with a hole that big I would be throwing in clean chunks of sharp rock or broken concrete as the mix is poured in to save on concrete. Just do not use brick.
    Bill D.

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    Thank you very much for the concrete amount information and some great ideas on preserving the post and how to go about it. I will order 6.5 yards. Gladly take more suggestions - the more I have the better decision I can make on the hay barn.

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    Unless you've already got 'em dug, those holes are bigger diameter than you need. For 6x6's a 12" hole is fine, 18 if you must. If you're set on those holes I'd use 8x8s

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    Default concrete?

    Are you using treated 6x6's? If so just put a round 3 or 4 inch thick concrete plate in the bottom of the hole to keep the post from settleing. the weight of the barn will hold it down.Then plumb and square up everything and fill the holes with fill dirt. built it 30+ years ago and it still there.
    Contracted the Amish to put it up,went 4 foot deep in michigan on account of the frost.
    jim

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    I'm surprised nobody has mentioned .7854 as the multiplicand. 4 keys in order on any keypad, and you got 2 foot D, = 4 Sq. Ft X.7854=Pi (3.1416)per foot of depth. 2 feet deep, 6.2832 CF less the volume of the post.

    I always use .7854. Much simpler than calculating the area of a circle.

    More esoteric methods also work, but I am less apt to use formulae. Easiest is the best and quickest.

    Cheers,

    George


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