We had a problem with the sidewalk. Last winter we had a lot of snow and when it melted we noticed that our sidewalk was sinking in on one end. Not bad, at least at first, but it got worse.
My husband asked around and got some ideas on how to fix it. It required a little elbow grease, but we got it done.
I dug under the edge of the low side and my husband jacked it up. Then we packed as much sand as we could under it. You will need to back fill with sand and small gravel, using a pipe or board to get it all the way under the slab otherwise it might not hold up.