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Foundation compaction

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HighHopes
Join Date: Sep 2010
Posts: 5 Santa Cruz Ca
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2010-09-09          173889


I need to dig a hole for my foundation and fill/compact it with ??? for a foundation. The hole will be 40 by 100 and four foot deep. I do not know what material to use and how to go about the compaction. Any help would be appreciated.





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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2010-09-09          173897


There are too many unknowns for a direct answer, such as what's under there, the structure's purpose and construction, and state/local building codes. You might talk with a local contractor or an owner of a similar structure. ....


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earthwrks
Join Date: Dec 2003
Posts: 3853 Home Office in Flat Rock, Michigan
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2010-09-09          173902


Auer's right but I'd like to add you should talk to a local building department official and a civil engineer or archiitect familar with your situation/conditions.

Generally speaking, you need to use a compactor to compact in what are called lifts---usually 3-4" thick layers of fill. BUT it depends on what type of fill you are using, moisture content, etc., etc. The four types of compactors are vibratory roller, plate-type, jumping jack, sheep's foot. Generally you cannot use one type of compactor for all conditions. There is another type used for trenches and that is a about a 4 - 6' wand with pressurized water which is injected into the area. Water displaces the air pockets and as the water drains away gravity pulls the soil down resulting in compaction. Nice to keep in mind when digging and refilling trenches since dirt tends to expand by 30% when uncompacted. ....


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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2010-09-09          173907


Quote:
Originally Posted by HighHopes | view 173889
I need to dig a hole for my foundation and fill/compact it with ??? for a foundation. The hole will be 40 by 100 and four foot deep.


Well, first off, you don't need to dig a hole nearly that size, normally you would just dig a trench where you want the walls to go and pour a footing (depending on building size and soil conditions) 12" - 36" wide and then build walls on top of that.

For example, if you dug a 4' deep hole 48' x 108' (to allow for working space) you would have nearly 800 yards of fill, that would be enough to fill 80 standard dump trucks.

If however you only dug a 4' wide trench for a 40' x 100' (280 lineal feet) footing and wall, it would only generate about 40 yards of material, that would only fill about 4 dump trucks.

Do you have a need for 76 dump extra truck loads of dirt somewhere? LOL

After you pour the footing and perimeter wall, you just pour a floating slab right on top of the existing soil unless there is bad soil conditions.

Best of luck. ....


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HighHopes
Join Date: Sep 2010
Posts: 5 Santa Cruz Ca
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2010-09-09          173912


My site is on a farm and the soil engineer has filed a report requiring me to remove the soil due to the organic material contained in it. I am putting in a slab foundation and that may be the reason she is requiring me remove and replace the entire house footprint of 40x100 amd she says the organic material was found down to four feet. I calculate 1,777 cu yds. I can dispose of the dirt on my property because I have 27 acres. What should I use to replace it to get compaction required for a foundation.
....


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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2010-09-10          173924


Quote:
Originally Posted by HighHopes | view 173912
I need to dig a hole for my foundation and fill/compact it with ??? for a foundation. The hole will be 40 by 100 and four foot deep.
[QUOTE=HighHopes;173912] My site is on a farm and the soil engineer has filed a report requiring me to remove the soil due to the organic material contained in it.


I am putting in a slab foundation and that may be the reason she is requiring me remove and replace the entire house footprint of 40x100 amd she says the organic material was found down to four feet.


I calculate 1,777 cu yds. I can dispose of the dirt on my property because I have 27 acres. What should I use to replace it to get compaction required for a foundation. [/QUOTE]

Well, as for the first & second paragraph, the engineer is (IMHO sort of) right, you can't support a building on organic material. However, she should also have told you that all you need to do is support the building on a narrow foundation that goes down past the organics to undisturbed soil, then make a floating slab floor that will sit on top of the organics just fine.

As for the third paragraph, you're math is a little off, a cubic yard is 3'x3'x3', or 27 cubic feet. So, 1,777 cu. yards multiplied by 27 is 47,979 cubic feet. If you divide that by 4,000 (40' x 100') you get 12'. I don't think you want a hole 12' deep. I think you missed one "dive by 3" in your equation, it should be 4' deep, not 3 times that or 12' deep.

As for the refilling question, you should be using a good, silt-free, subsoil, or 'B' granular, but I still say, unless you have a real need for soil somewhere, and a source of cheap (and I mean realllly cheap) fill, don't build this way, it will cost you a big bundle of cash mare than is required.


Best of luck. ....


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HighHopes
Join Date: Sep 2010
Posts: 5 Santa Cruz Ca
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2010-09-10          173925


Whoops! I did miss the divide by three and should only require 582 cu yards. I am stuck with this method of building because of the cost and time required to make a change. I have $55,000 invested in the plans, engineering, and permits. The permit process took two years and I have extended the permit for two years. Now at the end of a four year wait I want to get started on a shoestring budget.

I would like to use soil from my property for the compaction. I have an area where I can get the deep clean soil. Any thoughts? ....


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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2010-09-10          173926


What's the structure for? Doesn't sound like a residence but if it is, I'm not sure about a floating slab. If it's a utility building, what kind of floor?

If you or your neighbors have stone piles, you can toss big rocks on the bottom and add progressively smaller ones. ....


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HighHopes
Join Date: Sep 2010
Posts: 5 Santa Cruz Ca
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2010-09-10          173934


The foundation is for a 4400 sq ft house with a slab floor. We do not have access to stones. I can get soil that is free of organic material on my property. I will be looking into a change in the plans that would allow for a "structural" slab.

I will check with my structural engineer and my soils engineer. ....


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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2010-09-10          173937


Ok, first off, your math is still wrong. If you need to dig down 4' to remove organics, then refill it with "engineered fill", fresh soil which has been compacted in layers (called lifts) of (based on your soil) generally 4" at a time, you will need a hole probably 10' bigger in both directions that the building, so 50' x 110' x 4' deep or 22,000 cubic feet. There is 27 cubic feet (3'x'3x3') in a cubic yard. So, 22,000 / 27 = 815 yards of material.

As long as the soil meets with approval of the Engineer who has to sign off on the job, i.e. free of silt, organics, etc., it doesn't matter where it comes from.


Best of luck.

....


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earthwrks
Join Date: Dec 2003
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2010-09-17          174071


There are other hybrid options too.

Piers. Piers consisting of augered holes down to solid earth or rock filled with concrete. The piers would likely be spaced 6' apart filling the entire footprint. The floor could be poured monolithically with the piers. Load bearing walls could benefit from pier loactions.

Pilings. My builders license instructor built an entire house on pilings in swampy land (pre wetlands law). Pilings look like telephone poles and driven into the ground (sometimes 70') and terminate either at or below ground. The building is built upon them. This is very common in the South. However they drive them into the ground one atop the other with as much as 28' sticking out of the ground.

Grade beams and footers. Footers could be dug to stable ground. Rather than remove and not replace all the dirt inside, grade beams made of concrete connected to the walls and reinforced, lay in a trench at or just below grade. Grade beams would go under load bearing walls. And they would support the poured floor.

Basement. If you want more space and less cost to backfill, build it conventionally with wood or steel foor joists, and wood floor. ....


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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2010-09-17          174073


EW, I think you're forgetting about one little tidbit of critical information.

The OP "HighHopes" is located in Santa Cruz, CA., I doubt a few of your options would be allowed for seismic protection reasons, and if they were, it would add dramatically to the overall cost.

One of the reasons they like 'slab on grade' so much for seismic areas is that it makes the house sort of independent of the motion of the earth. It can sort of wiggle around on the surface, as opposed to being twisted when the above & below ground portions move at different rates and / or in different directions.

Best of luck.
....


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kthompson
Join Date: Oct 2005
Posts: 5275 South Carolina
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2010-09-17          174074


Murf you saying they want "Mobile Homes"? Never can think of any mobile homes in the south being damaged by earth quakes. Now drunk driver different story. :) ....


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SteelBldgPE
Join Date: Jun 2012
Posts: 3 Modesto, CA
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2012-06-22          183994


To fill the excavated area, search your own 27 acres for good soil. Then compact it as others have recommended.

Another option is to drill pier footings down to minimum 5'. An engineer will design the perimeter footing as reinforced concrete beams to span between the piers. This is most likely going to be the cheapest, easiest solution. ....


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