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The sidewalk leading up to my front door developed what looked like a sink hole under it about a year ago. Since then, an animal of some kind has made the hole even bigger and it now runs as a tunnel under my pathway.

QUESTION: How to I fill this hole most effectively? Obviously it would be great if I could do it cheaply and without busting up the sidewalk.

CONCERNS: I like in Omaha, NE. We have extreme winters and summers. I thought about pouring concrete into the hole, but I'm concerned that it would expand under the sidewalk and cause buckling and cracking. I also thought about filling it with just dirt and sand, but I'm concerned that I won't be able to get the hole filled directly under the middle of the sidewalk, thus not supporting the weight load put in the walkway.

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The final answer: both. I had originally intended to fill the hole myself with cement, but after I dug out the edges and poked my head in there, I noticed the hole was a lot bigger than I had originally thought it was going to be and there was a large void under the stairs. So I decided to pay for mudjacking to ensure it's properly filled. –  Snekse Oct 12 '10 at 3:20
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2 Answers 2

up vote 5 down vote accepted

Fill the hole with concrete. Concrete doesn't expand in the cold -- you're probably thinking of frost heave, which is where moisture in the soil freezes and expands, disturbing whatever's above it. If your sidewalk hasn't heaved by now, then the addition of new concrete below it isn't going to change anything.

Filling the hole with dirt or sand may in fact cause the heaving you're concerned about though -- I can imagine a situation where you're unable to properly compact the dirt underneath the sidewalk, creating a nice loosely-filled pocket for water to sit in and freeze.

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Thanks for the insight. Should I be concerned about frost heave expanding horizontally into the concrete that's under the sidewalk? My gut says no, but would like to hear your thoughts. –  Snekse Oct 4 '10 at 19:11
    
I don't know enough about it to say for sure that that wouldn't happen. But my gut, like yours, says it wouldn't, or at least not to a degree that would cause problems. –  Mike Powell Oct 4 '10 at 19:22
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A concrete leveling company could do the job. I hired a company to raise my driveway back to level. They drilled a small hole in the cement pad and pumped in hydraulic cement. It leveled out the pad and they assured me that it won't be bothered by frost heave. The leveling service might be your best option to ensure that the hole is filled. If that hole collapses it would put stress on the middle of the sidewalk (if the hole is large enough), causing it to split. This is pretty much what happened to my driveway, the ground sank only in one section and the strain on the corner of the concrete was too great and it split where the ground dropped.

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Our sidewalk is still level, so I won't need to lift it. I'll look into the hydraulic cement since it sounds like it doesn't shrink as much as standard concrete after it's poured. Thanks. –  Snekse Oct 4 '10 at 20:06
    
Just curious, how much did the leveling job cost? –  James Van Huis Nov 3 '10 at 19:49
    
@James I had my driveway leveled, so it was larger than a sidewalk. They leveled two 10' x 10' concrete pads and sealed all the cracks to the tune of about $800. Was actually a great deal considering the amount of sinkage that had taken place. I'm VERY happy with the work. –  Scott Vercuski Nov 3 '10 at 22:23
    
Thanks for the reply. I've got a frost heaved 2 car garage that I need repaired, but I have been hesitant to get an estimate (I figured it would be significantly higher than that). –  James Van Huis Nov 3 '10 at 22:40
    
@James I was surprised at the cost as well ... I thought it would be much higher. It was so reasonable that I'm having the same company come back and do some foundation repair for my within a month. –  Scott Vercuski Nov 4 '10 at 10:12
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