Author Topic: Post backfill  (Read 8336 times)

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Cody

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Post backfill
« on: November 15, 2007, 04:47:51 AM »
I built the 20x30 one story and now I need a storage/workshop shop. So I set 4x6 post into the ground  The problem is they are backfilled with the dirt that came out of the hole. The post are 40" deep and frost line is 30" but the soil we have here is silty clay loam with not rocky gravel or drainage and we have bad frost heave. Because it was a shop I didn't care but there is a good posibility it could end up as more living space. So is there an easy fix if the post frost heave or do I scrap it and start over. also at the bottom of the hole the post is sitting on a 12" round stepping paver. Thank You for your thoughts
- Cody

glenn-k

  • Guest
Re: Post backfill
« Reply #1 on: November 15, 2007, 07:19:40 AM »
Hi Cody.  I don't see an easy fix if frost heave has already been a problem.

Is it possible to keep the ground dry under there or does it get pretty wet and freeze solid too.?

I haven't been in an area with freeze problems so others may have better suggestions.


glenn-k

  • Guest
Re: Post backfill
« Reply #2 on: November 15, 2007, 07:47:17 AM »
Here is one pretty good article on it.

http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd128_e.html

and from here http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd026_e.html

Quote
If conventional foundation walls and footings are used for detached unheated buildings, the footings should be located below the level of maximum frost penetration. In such cases the backfill should be carefully selected and well drained. If this is not done, frost heaving in the backfill may occur that will lift the foundation wall because of the adhesion of the soil to the wall.

I see lots of soil in the background - Is digging down a foot or so around each of the posts, dropping a 30" piece of 8 or 10 inch plastic pipe around it, then raising the outside level of the ground up 18" to give you 30 inches that can't grab the post an option?  Straw bale insulation around the posts?
« Last Edit: November 15, 2007, 07:53:47 AM by glenn-k »

Cody

  • Guest
Re: Post backfill
« Reply #3 on: November 15, 2007, 08:01:15 AM »
Thank You so much for your quick response. Frost heave has not occured yet. but you mentioned exacly what I was concerned about. soil grabbing the post then pulling it up even though the bottom of the post is 10" deeper then frost.  So you think if I keep frozen soil from touching the post for about a foot or so deep that would work? once the biulding is built I plan on using pressure treated dementional lumber as a scirting and then backfilling a nice little slope.

glenn-k

  • Guest
Re: Post backfill
« Reply #4 on: November 15, 2007, 08:19:40 AM »
I was thinking of digging down around each post as far as practical and slipping a sleeve of plastic or other pipe over it to keep the frozen soil away, but extending the pipe the full 30 inches and backfilling soil around it -- looks like you have plenty of room there to do that.  This would still raise the freeze level up 30 inches so the bottom could not freeze and grab.  Plastic tight around the wood is not great as it locks moisture in to the wood.  Felt deteriorates underground and would not release well from the wood anyway.  A pipe sleeve could slide up without raising the wood.  

Your skirting and drainage could help.  Membrane under the fill could help keep the ground dry under the building also.  Slope before installing the membrane - such as 6 mil plastic then  balance of fill on top.

Gutter the roof water well away also.


Sassy

  • Guest
Re: Post backfill
« Reply #5 on: November 15, 2007, 08:28:36 AM »
Cody - glad to hear from you again!  I was wondering how you were doing.  Do you have anymore pictures of your home you built?  Don't think a lot of people have seen what you have done - it would be an inspiration to a lot of the women here on the forum... also the men who are just planning on building for the 1st time!!   :)   (inside pix, too, if you have them - you know we all like pictures!)
« Last Edit: November 15, 2007, 08:30:17 AM by Sassy »

Cody

  • Guest
Re: Post backfill
« Reply #6 on: November 15, 2007, 10:41:27 AM »
My mom is living in our house now, I didn't want to move out of town until I had the baby next month. I dont have very many pics I keep thinking I will get more but then I forget. so here is what I have of the inisde.
-Cody

Cody

  • Guest
Re: Post backfill
« Reply #7 on: November 15, 2007, 10:42:55 AM »
okay here is another one

Cody

  • Guest
Re: Post backfill
« Reply #8 on: November 15, 2007, 10:44:20 AM »
I dont know how to add more than one picture at a time - not computer savvy.


Cody

  • Guest
Re: Post backfill
« Reply #9 on: November 15, 2007, 10:46:01 AM »
last one

Sassy

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Re: Post backfill
« Reply #10 on: November 15, 2007, 12:11:27 PM »
You are an amazing woman, Cody!   8-)  You should be really proud of what you've accomplished & only one more month until the baby is born!  A real pioneer  :)  Looks really nice, I am impressed!

glenn-k

  • Guest
Re: Post backfill
« Reply #11 on: November 15, 2007, 12:39:05 PM »
Looks great Cody- good job.  

Picture info and tutorial is in the Forum News section.  It's easy to do - MountainDon walks you through starting a free Photobucket account and posting multiple pictures here.

jraabe

  • Guest
Re: Post backfill
« Reply #12 on: November 15, 2007, 08:57:43 PM »
The house project looks quite nice and very comfy. Good work!

The workshop post foundation with a clay soil backfill around the posts could be a problem in freeze thaw cycles. Frost might lift the posts and then let them drop back down on the footer pads when the weather warms. This could mean something as small as a door or two binding from time to time... or something more detrimental if things shift and move more over the longer term. It is hard to tell at this point. Frost action is very powerful and can move things sideways too if one side typically freezes while the other stays warmer.

A post and pier foundation is generally not recommended in wet clay soils unless the foundation piers can be drained or otherwise protected against expansive soils.

Are the posts foundation grade pressure treated? If not, in 15 to 20 years, you (or the owner then) can jack up the building and put a permanent foundation under it. It's done hundreds of times a day all over America.
« Last Edit: November 15, 2007, 09:00:19 PM by jraabe »

Cody

  • Guest
Re: Post backfill
« Reply #13 on: November 16, 2007, 03:48:42 AM »
yes the posts are cca .60 retention. I wish I had just planned alittle in advance. It was a case of the guy with the auger showing up and saying are you ready? The thing is he is pretty crippled so  I had to set the post myself wile he backfilled and I dont think they are very square either. I hope I can make a square deck out these post maybe being off a couple inches.  All this wouldn't matter except he also layed down electrical and water lines so  I began thinking it might make a good second house sinse my mother moved into the 20x30. It is supposed to get down to 26 degrees in a couple days so I will look for frost heaving. Im thinking i can mark a line at ground level and if it rises out or moves then it heaved?
Thanks for everything and all your advise to everyone - Cody


Cody

  • Guest
Re: Post backfill
« Reply #14 on: November 16, 2007, 03:53:09 AM »
I just wanted to ask if anyone knew about rubble trench foundations. Im looking online as a second do- it yourself choice but?? I especially want to know about uplift and clay soil? - Thank You

glenn-k

  • Guest
Re: Post backfill
« Reply #15 on: November 16, 2007, 05:38:22 AM »
There may be other ways to do them - rubble is usually various sized rocks in a slurry of concrete.  I have also seen dry stacked rubble in a trench under rammed earth etc. called a rubble trench foundation.  So it is usually a way to use local waste rock in the foundation.

For use where there is expansive soil - and where code is not an issue, then you would be able to use common sense.  So...

To stop the uplift with loose rubble - even if a grade beam was poured on top, I would dig the trench at least to the bottom of the freeze level and if in a hilly area, continue the drain side of the rubble trench down hill or at least make sure it can gravity drain to daylight downhill - install pipe if necessary - dry wells could work also depending on circumstances.  Make all trenches slope a bit toward the drain. 1 or 2% should do.

If using the form method, I would set the inside form plumb vertically, and set the outside form on a taper at least until it got to a bit above the surface - maybe an inch and a half per foot to 2 inches per foot as ice expands about 10% so it would take that amount to stay free.  A double #4 -  1/2 inch rebar bottom about 3 inches up -- ends lapped 20 dia. min  would keep things together and one bar in the top of the stemwall would keep it together.  Usually 3 inches in from the outside and 3 inches up or down from soil contact on the rebar.  Prop the bottom ones with rocks or concrete chunks or dobies.

When the soil freezes anb the water in it turns to ice - (rock) -- it will slide up the sloped footing breaking free as it expands.  I left out the fill the forms with rubble and pour mortar between the rocks part.  You would also shake or- prod with a stick etc to get the mortar to flow around the rubble and give you a smooth fill between the rocks and the form.  Once above the ground you could continue up with an 8" stemwall or rubble stemwall with both straight sides if you wanted or if easier and not a lot of variation in height You could work out the taper to give you the 8" top width -bottom 1' minimum for single story I believe..  Narrower stemwall may work -8" is used in a lot of cases.

This is my opinion of something that should work -- others may have better ideas. :)

Offline coryjohnston1980

  • Newbie
  • Posts: 1
Re: Post backfill
« Reply #16 on: July 19, 2010, 01:12:47 AM »
Cody, I am courious how you got all the panels to meet up once on site. I live in town right now. I just bought some land in western kansas and would love to find out how you did it. Just a side note I will be building on a peer/beam foundation. Could you please let me know how you did it? My email is coryjohnston1980@yahoo.com thanks
Cory Johnston

 

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