# Foundation on disturbed soil



## Bud9051 (Nov 11, 2015)

Not a pro on this but recall seeing many locations where the lots were created using lots of fill. The difference was, they waited several years before building. 5 years comes to mind. So, I'll watch to see if anyone knows if the time factor can change the "disturbed soil" condition in the report.

Bud

Note, I would also be curious as to what they used to fill in that area, sludge, demo debris, or whatever.


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## SPS-1 (Oct 21, 2008)

Best I can remember, the required time I have seen to be consider "undisturbed" is 10 to 20 years. Don't think you can just say enough years have passed. Would need to do testing to prove it. Any foundation on these lots will need a P. Eng's stamp.


I remember driving by when they did the rehab a couple of years ago. Dug pretty deep to get some underground water tanks/pipes out. It all looked like local soil (which has high clay content around here) to me.


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## Nealtw (Jun 22, 2017)

SPS-1 said:


> Best I can remember, the required time I have seen to be consider "undisturbed" is 10 to 20 years. Don't think you can just say enough years have passed. Would need to do testing to prove it. Any foundation on these lots will need a P. Eng's stamp.
> 
> 
> I remember driving by when they did the rehab a couple of years ago. Dug pretty deep to get some underground water tanks/pipes out. It all looked like local soil (which has high clay content around here) to me.


 We have lots on questionable soil whether disturbed or old mud slides. 
It is not unheard of digging out as deep as 30 ft and re filling it with compactable fill.


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## MTN REMODEL LLC (Sep 11, 2010)

I would not be scared of caisson's..... (apart from cost differentials) if done with proper engineering, as good or better than building on undisturbed soil that really has not been engineered.

We heli-jacked a home in SoCal.... alot less support than caisons.... and have no problems for over ten years....


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## Canarywood1 (May 5, 2012)

I doubt they would drill caissons for a foundation a little over 13 feet deep.


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## stadry (Jun 20, 2009)

*push piers under steel reinforced conc grade beams,,, normally push piers are stronger than helical piles - at least here in atl,,, nobody's setting caissons for something like this NOR would anyone pay for it*


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## Canarywood1 (May 5, 2012)

Pros and cons for both uses, push piers are used on heavy structures, but should not be used on a single story home, helical piles would be the ideal use for that application , but they could not be used on a heavy structure.


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## Nealtw (Jun 22, 2017)

He can ask for an engineers report on the property or get permission to dig a hole and assess the soil himself or with his own engineer, how deep is the disturbed and what's under it.


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## Nealtw (Jun 22, 2017)

https://buildingadvisor.com/buying-land/site-characteristics/slope-soils-water-vegetation/


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## Canarywood1 (May 5, 2012)

Nealtw said:


> He can ask for an engineers report on the property or get permission to dig a hole and assess the soil himself or with his own engineer, how deep is the disturbed and what's under it.




OP states there is already an 80 page engineering report posted .


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## Nealtw (Jun 22, 2017)

Canarywood1 said:


> OP states there is already an 80 page engineering report posted .


 Forgot about that.:biggrin2:


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## ZTMAN (Feb 19, 2015)

If you really like the lot, send the geo tech report to a screw anchor company. They will be able to assist you.
Generally the helical piers are placed six feet on center under the footing. In this case, interior piers will most likely be needed as well.
In the north east US it seems like that the price per pier averages $1,100 which price is good to 17 feet and then they charge a per foot price after that.
Your price will depend on how big of home you want to build but generally for a 2000 sq. ft. foot print, I would guess some where between $70k and $80k.

Most companies do give a lifetime guarantee against settlement


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## SPS-1 (Oct 21, 2008)

Yes, helical piers would be a possibility. Suppose I am old fashioned - I like concrete (proven for a couple thousand years), but helical piers would seem to make sense for something like this. One builder told me about $C1000 - 1500 per hole and guessed at 20. I have the names of a couple of local P. Eng's around here.


Interesting (good) to hear that they give a lifetime guarantee. But the devil is in the details ---- If the house moves what does the guarantee mean --- that I get back the $500 that each steel auger cost?


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## AndyGump (Sep 26, 2010)

It seems as if a Post-tensioned slab would work well in this situation.

Andy.


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## ZTMAN (Feb 19, 2015)

SPS, the guarantee means they will come back in and address the issue. Those piers can actually lift the house if needed.
Look at some of their demo videos if you have not seen them installed.


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## stadry (Jun 20, 2009)

*here in atl, push sells for $1,500 ea,,, after 6, there's usually a discount,,, most guys sell a min of 3 or walk*


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## firehawkmph (Dec 12, 2009)

I wouldn't rely on a time factor to determine if soil is "undisturbed" or not. I have built houses on lots that were filled 40-50 years prior. We dug down deeper til we hit undisturbed soil. Most of the layers above were not compacted and of poor quality. We have also had to drill caissons for the type of lot that falls off towards the back. Had soft soil where the footers would normally sit. It wasn't a big deal to do. Best to really know what your getting into before you buy.
Mike Hawkins


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## MTN REMODEL LLC (Sep 11, 2010)

^^^^^^^^^^^^^^^^FIREHAWK^^^^^^^^^^^^100%

I'm with FireHawk as to using time as a measure of compaction.

I added an addition on a sloped lot that had been there probably 20+ years.

It was a subdivision, and became apparent that it was a heavily graded fill.... easy digging after 20+ years .... we had to go down until we found undisturbed for spread T footers.

And on my sons lot, we actually went to helical jacks.... that land had been there well before america was discovered. Soils engineer explained that it likely in a former river bed.


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## SPS-1 (Oct 21, 2008)

I got lucky with the engineers I talked to. First guy basically said (when translated in English) that he was not interested in my little consulting job. Second engineer I called, turned out to be the chief engineer on the project to rip out the underground services a few years back. So he knows that property like the back of his hand. Yep, a lot of that area had been dug up pretty deep. Without doing a full analysis, he said he probably would go with helical piers. 


Basically, I would have to figure on adding $20k-$30K to the cost of a standard foundation. 


City has already paid for an engineering study that says this area is soft, so no way they are going to issue a permit for a house with a standard depth foundation that does not address this.


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## Canarywood1 (May 5, 2012)

Well you got the answer from the horses mouth , and as i stated before in all my years in the industry, i've never heard of caissons being used on a single family residence, and doubt i ever will because of the cost factor, bad enough on helical piers.


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## SPS-1 (Oct 21, 2008)

Oh yeah, so 60 Minutes tonight is re-running the story about the skyscraper in San Francisco that is sinking and tilting. That makes me feel better. :wink2:


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## Nealtw (Jun 22, 2017)

SPS-1 said:


> I got lucky with the engineers I talked to. First guy basically said (when translated in English) that he was not interested in my little consulting job. Second engineer I called, turned out to be the chief engineer on the project to rip out the underground services a few years back. So he knows that property like the back of his hand. Yep, a lot of that area had been dug up pretty deep. Without doing a full analysis, he said he probably would go with helical piers.
> 
> 
> Basically, I would have to figure on adding $20k-$30K to the cost of a standard foundation.
> ...


 I would still want to know how deep it is, replacing it with compact gravel may be cheaper.


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## SPS-1 (Oct 21, 2008)

Well, I did end up buying that lot, and I closed on a house on that lot today. 

Turned out we only had to dig a couple of feet deeper to hit solid soil. But you might be amazed at how much time and money you can spend just digging a couple of feet deeper. So footings go down to solid soil and basement slab is sitting on a couple of feet of compacted gravel. Garage and terrace (back porch) slab are on maybe 8 feet of gravel. I am in no hurry to pour the driveway --- let the ground settle through another winter. 

But at least its finally done. And a lake view that reminds me why I did it.


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