How to fill large void under concrete slab?

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  #1  
Old 04-11-19, 02:16 PM
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How to fill large void under concrete slab?

There is a large void under the slab of the garage where it meets the asphalt parking lot. Not really sure how the void developed but the opening to it is as big as your foot, and it's size I would guess in the one cubic yard range. I guess I could fill it in with sand or gravel but that wouldn't get it all the way to the top. What about expanding foam like: https://www.youtube.com/watch?v=gWJvrhZlzaM Is this a DIY fix? If not, what companies do this service?
 
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Old 04-11-19, 04:57 PM
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Expanding foam would be my choice. You'll have to search for companies that perform the service. I did it as a DIY and was pretty easy.
 
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Old 04-12-19, 04:16 AM
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If you go with a co. that does this get several estimates. I had some work done and got estimates ferom 500 to 4000.Works great.
 
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Old 04-12-19, 05:19 AM
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Not sure how the expanding foam will will perform out in the sun and weather. If you fill it with gravel and tamp it through the opening you mentioned it will move towards the far end of the hole. Even if it doesn't fill it completely it will fill in front and provide support.

Once you use an expanding foam it could become very difficult to do more filling should erosion continue.

Bud
 
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Old 04-12-19, 05:49 AM
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I agree with Bud in regard to being able to tamp fill through the hole, but my choice would be pea stone over sand or gravel as it will flow easier and provide better compaction. I think you would find that would provide pretty substantial support by itself, but could always cap it with a lesser amount of foam if you wanted to.
 
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Old 04-12-19, 07:12 AM
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I'd start by figuring out where the material went to create the void...

Limestone in the area? Could be a tree stump that rotted out, or a contractor using frozen dirt for fill.

I'd start by dumping a bag of dry concrete mix down the hole, yes dry mix, no water.

Get around 3 feet of tubing, either old car brake line or perhaps plastic compression tubing. Place that in the center of the hole.

Get a cubic yard of 2A (clean 2" stone). Backfill the hole with stone, around the tubing.

Get a big can of expandable spray foam, securely connect the foam nozzle to the 3 foot tube, and trigger the foam.

The expandable foam will slowly spread out THROUGH the gaps in the 2" stone, both lifting the stone up from the bottom, and creating a "foam-crete" of stone aggregate held together by the foam.

Pull the tube out, or cut off at the surface.
 
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Old 04-12-19, 08:36 AM
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First step definitely need to figure out where the material went.

It didn't just disappear it some how was washed away.

Once that is resolved and if you have a 1' dia opening, start shoveling in sand and small gravel, fill about 4" then hose it down to compact.

Repeat as many times as needed to fill the cavity!

By watering it down it will remove air, compact the material and you should be able to fill completely.

Since you have a hole you may have to open up some but it's going to need repair anyway!
 
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Old 05-08-19, 05:28 PM
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Just getting back to this and stuck a camera into the hole.



 
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Old 05-09-19, 05:13 AM
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Holly cow! That's quite a hole. To save on foam cost I would fill in the hole with clean crushed stone like #57. Stone like that naturally assumes a relatively high compaction. Then use expanding structural foam for the last 4-6" at the top.
 
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Old 05-09-19, 05:29 AM
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That's about what I was thinking too. I see Lowes has 0.5 cu ft bags of gravel. https://www.lowes.com/pd/Sakrete-0-5...vel/1000489233 Probably need about 10 bags.
 
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Old 05-09-19, 10:06 AM
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What you linked appears to be pea gravel. You do NOT want that. It does not compact or "firm up" unless completely contained. It tends to just roll around like a bag of marbles. You want a crushed stone that has jagged edges.
 
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Old 05-09-19, 10:26 AM
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OK I'll make sure of that.
 
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