Anyone have experience with "concrete raising"?

[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.
http://youtu.be/inTMdUt41lM

[ckissick]

I'm a geotechnical engineer. Mudjacking works great. It should work, but having not seen the site, I can't say for certain.

If the driveway is on a thick fill, but the building is on deep piers, the driveway will settle while the building will not. After mudjacking, the soil might continue to settle, and you'll have to repeat the process. But if it's just poorly compacted base rock, the settlement should be finished.

How's the weather been? If you've been having a drought, then expansive soil may have dried out and shrunk, making the slab sink. The building, if built right, won't sink. This is not a likely scenario, but I just thought I'd mention it.

[Paul_Heery]

Thanks for the reply. The weather has been horrible. We just had a winter with record snowfall and it seems like it has been raining forever lately.

I am meeting with one of the potential contractors on Saturday. Anything specific I should be asking him?

[wdfifteen]

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.

[Paul_Heery]

Originally Posted by wdfifteen

It sounds like they poured the sidewalk on top of the backfill without preparing a stable foundation for it first.

I believe that is probably the most likely explanation. So, I guess your vote would be for option one.

[wdfifteen]

Originally Posted by Paul_Heery

I believe that is probably the most likely explanation. So, I guess your vote would be for option one.

If it was my home and I intended to stay in it for a long time, I would go with option one plus stabilizing the soil under the walk. If you're leaving in two years, jack it up. There is also the possibility that it has finished settling and the mud jacking will take care of it permanently. If the backfill is shallow it may have finished settling, if there are several feet of it, it won't stop for a long time.

[E38Driver]

To make a long story short, my house tipped two inches from the front to the back and they had to mud jack my house back to level. It works. It has been two years and no change. They also had to do lots of other work before they leveled the house but the system does work.

Dave

[dad911]

If you remove and replace, the contractor can use rebar to dowel the new slabs into the steps so they won't move again.

[Garp]

Originally Posted by E38Driver

To make a long story short, my house tipped two inches from the front to the back and they had to mud jack my house back to level. It works. It has been two years and no change. They also had to do lots of other work before they leveled the house but the system does work.

Dave

I'm just looking into this for an annex which has tipped. The house stands on poles but I was a cheapskate and only poured a slab since there's only a wooden groundfloor construction on it. I received an offer for a chemical lifting (PU).