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We got a house where it has a one foot strip of concrete that is 20 feet long besides a patio that is in good condition.

On this 1'x20' strip there are two spots where the concrete has risen about an inch. This has produced two humps and a lip next to the patio near these parts. (sorry no picture but won't be over to the house for another month again)

I dug around these areas and both were caused by roots from a tree 15 feet away. I have broken these roots out and have a good 3 foot hole along the ridge. Is there anything I can do to sink these two "high" areas to "flat"? Really willing to try anything, as if we can't I will just make my ridge hole bigger and dump concrete in.

  • Can you access the soil under the strip of concrete? – isherwood May 9 '16 at 16:49
  • @isherwood - Very dense compacted soil. Nothing rock or anything else. – DMoore May 9 '16 at 17:05
  • @isherwood - sorry. Yes very accessible. I have it dub out and it looks like a layer cake right now. Just need to send word to workers on what to do. – DMoore May 9 '16 at 17:30
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In your shoes, I'd do this:

  1. Trench out along the concrete strip to give yourself access to the soil under the raised portions of the strip. Make the trench 6-8" below the bottom of the concrete and wide enough to work in.
  2. Determine whether there's remaining root under the concrete. If so, dig and chop it out completely.
  3. Using a water hose, begin "drilling" under the high spots in the slab, allowing the water to wash soil out into the trench. Do this every foot or so. Rather than completely removing the soil in any large areas, remove it from several small areas. This will result in more predictable settling.
  4. With a heavy object padded with towels or plywood, tamp the concrete down as you flush soil out from underneath.

Some notes:

Be sure to get the hose all the way to the far side of the concrete strip to accomplish a uniform descent and prevent tilting.

Stop when the slab is about 1/2" above the adjacent concrete. Chances are the slab will settle further as the soil fills the holes back in over time. Do occasional tamping over the next day or two and see where it stabilizes. Remove more soil if necessary, down to 1/8" or so above the adjacent slab.

  • I would back fill with sand and use water to flow the sand into the voids once the majority of leveling is done. – Ed Beal May 9 '16 at 18:34
  • Sure, but ideally none would be required. – isherwood May 9 '16 at 18:35
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For 20 square feet of concrete I would simply saw it off the adjacent patio if the strip is not a separate pour and then break out the strip with a jack hammer. Haul that away and then re-prep the base for new concrete. In the case of the tree roots just chop them out of the way.

This will give you the cleanest solution with the longest life. Trying to settle a buckling strip seems like a lot of work that may not really lead to a long lasting solution.

  • Cut it up, yes. Undermining it sounds like a can of worms. I re-leveled a side walk once: cut them apart, flip them out of the way, re-grade adding gravel fines, tamp, replace. – Mazura May 10 '16 at 18:07

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