How do I fill a hole under a sidewalk?

Question

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.

Answer 1

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.

Answer 2

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.

Answer 3

I would use polyurethane 2 part spray foam and fill from one side to the other. Cures quickly, can be trimmed once cured and is waterproof. I had several voids filled quickly and easily in a short time. Concrete Jack is the leader in the field but there are many others. BTW it is very durable and supports loads well. It has been used to level concrete on interstates.