Quote:
Originally Posted by Paul_Heery
I need to solicit advice from the collective.
We are in a townhouse development that is about six-years-old. I happen to be on the board. We have a situation where the concrete slabs that make up the sidewalk at the entrance to about twelve of the units have sunken into the ground. This has left a gap between the pre-cast concrete steps and the sidewalk that varies from 1 to 2 inches. The steps are attached to the building foundations and they have not moved. It is clearly a problem with the slabs sinking into the ground.
We have been looking at the repairs and we have two options.
The first option is to have the slabs broken up and removed. Then, have new slabs poured.
The second option is to have the concrete raised. From what I understand, it is also called mudjacking. This is a process where holes are drilled in the slab and a slurry is pressure fed under the slab to raise it up. This approach is much less disruptive and considerably less expensive than option one. Any experience with this? Any things to look out for?
Thanks.
Here is a video that shows how it is done.
YouTube - Concrete Repair Tips - Mudjacking and Slabjacking Techniques |
It sounds like they poured the sidewalk on top of the backfill without preparing a stable foundation for it first. It has happened a lot in the subdivision near me. Some people here broke up and replaced the walks after four or five years but didn't address the underlying problem, so they have continued to sink - most have gone down about another inch as far as I can see and seem to have stopped settling.
What you describe is called slab jacking around here and it would probably have the same result as replacing the walks without building proper support under them.
I think the correct way to pour a walk on disturbed ground is to dig down to the undisturbed grade and backfill with gravel to the level you want the bottom of the walk. That would be the permanent way to fix it. There may be some kind of soil stabilizer or compaction method that has come into use since the last time I had to pour a walk.