#1  
Old 10-11-2012, 06:01 PM
Laborer
 
Join Date: Jun 2009
Location: Westchester
Posts: 86
Default uh oh...

I had someone else make my foundation slab when they did various stone
work around our house 3 years ago. I just noticed there's significant
erosion of earth around the slab on 3 sides, which has lead to
significant erosion of the slab. I guess it wasn't made deep enough
into the ground. (see pics) Is there anything I can do to stop the
erosion? Should I put mortar around it? Dig a foot down all around and
pour concrete?
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  #2  
Old 10-11-2012, 06:16 PM
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Il Pizzaiolo
 
Join Date: Oct 2009
Location: Ausitn
Posts: 2,861
Default Re: uh oh...

Backfill it with dirt, pack it in and plant grass or mulch to prevent the erosion.
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  #3  
Old 10-11-2012, 06:23 PM
Il Pizzaiolo
 
Join Date: Jun 2009
Location: So. Orange County, CA. USA
Posts: 1,155
Default Re: uh oh...

Jim, It's a bit tough to tell but it doesn't look too bad.. Yet.
How are you going to finish the area?

I think you could delay finishing the area for a bit while you finish the dome, but I'd want to get something temporary down that will stop further erosion. Gravel or what we call Base around here. Base is a rough sandy material that can be compacted and Concrete would then be poured on top. If you put down base and compact it enough to stop the continued erosion then when you finish the WFO the cleanup and prep for a patio is simple.

Chris
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Old 10-12-2012, 07:02 AM
Laborer
 
Join Date: Dec 2009
Location: Milton, Ontario
Posts: 97
Default Re: uh oh...

It looks like the concrete was honeycombed, which tends to happen when it isn't mixed properly and/or not vibrated. It is probably not important structurally, especially if they used rebar under the walls.

As suggested, I would just backfill.

By the way - sorry to say it but that concrete work looks sloppy and amateurish. I would not hire these people again.
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Old 10-12-2012, 02:30 PM
Peasant
 
Join Date: Jan 2009
Location: New York
Posts: 26
Default Re: uh oh...

Jim,

I can't tell for sure, but it looks like that is a slab on grade. Otherwise you should not see jagged edges.

I live in NY and dug down 36+ inches to avoid frost heave.

It appears as though the slab is higher than the surrounding ground by using gravel under it. This will help drain water, but the only way to be sure that the foundation will not crack or heave in a northern climate is to lay a footing below the frost line. A lot more work and expense to be sure.

You might get away with slab on grade if the water does not puddle underneath the slab.

Doug O
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  #6  
Old 10-13-2012, 12:59 PM
Master Builder
 
Join Date: Mar 2008
Location: Washington State USA
Posts: 768
Default Re: uh oh...

Three years since the slab was poured and it is still level...I would go for it. I don't see erosion but folds where the plastic upon which it was poured caused wrinkles on the edges. Yes, the slab could have benefited from vibrating but most slabs don't get vibrated. Slabs can be floating although the building department doesn't like it for structures...your driveway is a floating slab. Launch ramps are free floating and oft times poured over soft mud. Design should reflect intended purpose. While WFOs are heavy they work out to not very much in the way of pounds per square ft.

Frost heave seems to be a concern seeing as you live in upstate NY. Frost heave is funny in that it sometimes effects some structures and others nearby will be fine. Localized drainage is important and it seems the layer of crushed rock beneath the slab is providing it....I would be wary of compacting soil tightly around the base and thereby possibly trapping water beneath the slab. Free floating slabs usually are not as effected by frost heave if they have good drainage beneath them.

I was a QC on the Trans Alaska Pipeline System (TAPS). One of the items I was responsible for inspecting in my area was the installation of the Vertical Support Members (VSMs). These were 22 inch diameter pipes sealed on the bottom and filled with sand and two ammonia refrigerant pipes. Their length was computed by a program which took into account the soil type as the hole was drilled. After being placed each VSM was backfilled with a sand slurry. A "bent" consisted of two VSMs with a cross member which supported the 48 inch pipe. These were installed where the pipeline ran above the ground. The pipeline ran above the ground because of permafrost and fear that the heat of the pipeline would melt the permafrost. There were simple ammonia refrigerant systems in each VSM to keep the permafrost frozen year round. Even so occasionally a VSM would "jack". The power of the jack is amazing. In dealing with the problem the offending VSM be cut off, a new VSM hole drilled and installed and a wider cross bar placed. Most times this cured the problem, but on a regular schedule people had to return to the original VSM and cut it off as it would continue to jack out of the ground. It didn't happen often but when it did it was a serious pia. Telephone poles have been known to jack until they are standing with their end at ground level and simply fall over.

Just my 2 cents,
Wiley
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