#1  
Old 06-26-2012, 03:38 PM
bluecrow's Avatar
Peasant
 
Join Date: May 2012
Location: NY
Posts: 36
Default gravel and slab on soft soil?

I am re-siting my oven (due to dubious planning on my part) a few feet from an existing slab to a soil area that was filled and tamped 10 years ago. However, after digging one foot I can push a piece of re-bar down about 3 feet in some places.

Is this one of those "piers with feet -then a reinforced slab" situations, or is a floating slab on a couple of feet of gravel or concrete blend a possibility?

The oven will be a 36" Pompeii.

Don
Reply With Quote
  #2  
Old 06-26-2012, 04:18 PM
texman's Avatar
Master Builder
 
Join Date: Nov 2009
Location: Amarillo, Texas
Posts: 592
Default Re: gravel and slab on soft soil?

Is it in a low spot that has been wet or holds water? Is that typical soil stability in your area or is this spot different than surrounding soil?
Tex
__________________
My Progress:

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote
  #3  
Old 06-26-2012, 04:28 PM
Neil2's Avatar
Il Pizzaiolo
 
Join Date: Oct 2006
Location: Vancouver Island
Posts: 1,374
Default Re: gravel and slab on soft soil?

"However, after digging one foot I can push a piece of re-bar down about 3 feet in some places. "

I don't know exactly how hard you can push, but this sounds to me like very weak soil conditions.

Placing a slab on grade would likely give you some serious settlement problems. I would be tempted to continue to dig a test hole (rent a hand held posthole digger) down to firm ground. If this firm ground is in the order of 4 feet or so (or is uneven, i.e 3 feet at one corner, 5 feet at another), I would opt for a pile/pier type construction with a suspended slab.

If you can get some local expertize this would be good. It is worth fussing around at this stage.

Last edited by Neil2; 06-26-2012 at 04:38 PM.
Reply With Quote
  #4  
Old 06-26-2012, 08:23 PM
bluecrow's Avatar
Peasant
 
Join Date: May 2012
Location: NY
Posts: 36
Default Re: gravel and slab on soft soil?

Thanks for the replies. A bar cannot be pushed down so easily in typical soil conditions here (glacial drift). The specific area was beneath a garden bed and has suffered little traffic since fill leveled the space. It was formerly a hillside. I probably have firm ground at 4-5 feet. I'll check tomorrow.

If so, is the procedure to pour four footed piers with re-bar, then gravel up to the tops of the piers, then a reinforced slab tied to the piers?
Reply With Quote
  #5  
Old 06-26-2012, 08:38 PM
Tscarborough's Avatar
Il Pizzaiolo
 
Join Date: Oct 2009
Location: Ausitn
Posts: 3,143
Default Re: gravel and slab on soft soil?

I am not an expert on frost conditions living where we do not get more than a couple of minor freezes a year, but my understanding is that you have two options:

Dig down below frost level, which could be 4' in NY, pour a footing and then build stem walls to finish grade and pour a suspended slab.

Excavate below frost level, fill with compacted sharp gravel and build a floating slab.

A piered structure would have to be engineered which is normally beyond the scope of an oven. There are other designs using insulation and floating slabs with less fill, but they also have to be engineered.
Reply With Quote
  #6  
Old 06-26-2012, 09:06 PM
Faith In Virginia's Avatar
Master Builder
 
Join Date: Oct 2010
Location: Virginia
Posts: 720
Default Re: gravel and slab on soft soil?

Don't go for the slab on fill dirt. If you get unlucky enough to get half on the fill and half on undisturbed soil you will have problems that won't quit. I have run across this a lot especially with homes on basements. You would need to dig down 10' just to find something solid. You can dig deep piers down to something solid is one option but once you get past the 4' mark and your still on fill the piers will be a real challenge. One thing you can do if your fill is deep is get some 10' sections of galvanized pipe and drive them like a fence post into your loose soil. Drive them hard until they find something solid and won't go any more. If they don't go all the way in cut them at a level that will allow you to incorporate them into the slab.

The other way its to move the oven to solid ground. I would take this option if possible.
Reply With Quote
  #7  
Old 06-27-2012, 12:55 PM
Neil2's Avatar
Il Pizzaiolo
 
Join Date: Oct 2006
Location: Vancouver Island
Posts: 1,374
Default Re: gravel and slab on soft soil?

Three piers not four. (Four is statically indeterminate).

See my build for details:

http://www.fornobravo.com/forum/f21/...ucer-3033.html (Flying Saucer)

As Tscarborough notes, the reinforcing transition from the piers to the suspended slab is not something normally done in oven builds, but if you are competent in placing and bending rebar and in concrete pours this is an option.

Last edited by Neil2; 06-27-2012 at 12:57 PM.
Reply With Quote
  #8  
Old 06-27-2012, 01:23 PM
bluecrow's Avatar
Peasant
 
Join Date: May 2012
Location: NY
Posts: 36
Default Re: gravel and slab on soft soil?

Thanks for all the sage advice. I researched and read about some of the possible solutions. ( I am trained in geophysics, but not an engineer). None seemed achievable for a site beyond the reach of machinery. I can move the oven site to a 50 year-old, 6 " reinforced slab. I know that the concrete is very strong, and reinforced, because I had to cut some pieces out a few years ago.

I need to level the slab a bit, so I am researching steel and concrete options for leveling, now.

Don
Reply With Quote
  #9  
Old 06-27-2012, 09:30 PM
Apprentice
 
Join Date: Sep 2010
Location: Mesa, AZ
Posts: 235
Default Re: gravel and slab on soft soil?

Is there any reason you can't simply use self leveling compound. Under the oven itself you could probably work out an inch or two just with mortar joints on the block.
Reply With Quote
  #10  
Old 06-28-2012, 11:04 AM
bluecrow's Avatar
Peasant
 
Join Date: May 2012
Location: NY
Posts: 36
Default Re: gravel and slab on soft soil?

I was checking the compressive strength of the leveling compounds. My local masonry supplier thought a portland mix with fine sand would be okay as a leveler.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Gravel Base for Foundation Slab Question clofgreen Getting Started 4 10-17-2011 04:38 PM
A hello and a beginner slab dimension question sephora2011 Getting Started 3 06-28-2011 11:05 AM
Footers or Slab BeanAnimal Getting Started 19 04-01-2011 10:20 AM
Foundation gravel question kebwi Tools, Tips and Techniques 1 09-16-2009 11:03 AM
Concrete slab size pisc78 Pompeii Oven Construction 3 01-23-2008 06:03 PM


All times are GMT -7. The time now is 12:16 AM.

Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
2006/10 Forno Bravo, LLC