foam jacking a slab on grade adjacent to a retaining wall
foam jacking a slab on grade adjacent to a retaining wall
(OP)
I have a situation where foam jacking (pumping expansive polyurethane foam under the slab to lift the slab) is being proposed to lift a slab on grade that has settled behind a retaining wall. Should I be concerned about possible lateral pressure on on the retaining wall from the foam? The wet weight of the foam? The injection pressure? The expansive pressure? My gut tells me that the pressure is minimal, but I have not been able to find any references addressing the issue.
A few additional details... The retaining wall is an 8" thick cip concrete wall 10.5 feet high. The slab is 10'x10'x12"thick bearing on backfill on the retained side of the wall. The edge of the slab opposite from the retaining wall has settled about 6-8 inches. The edge of the slab on the retaining wall side has not settled at all because it actually bears on the top of the retaining wall. One corner of the slab opposite from the retaining wall has a post on it that supports the corner of one floor and a roof above (about 100sf of each). There are no other loads on the slab except foot traffic.
A few additional details... The retaining wall is an 8" thick cip concrete wall 10.5 feet high. The slab is 10'x10'x12"thick bearing on backfill on the retained side of the wall. The edge of the slab opposite from the retaining wall has settled about 6-8 inches. The edge of the slab on the retaining wall side has not settled at all because it actually bears on the top of the retaining wall. One corner of the slab opposite from the retaining wall has a post on it that supports the corner of one floor and a roof above (about 100sf of each). There are no other loads on the slab except foot traffic.






RE: foam jacking a slab on grade adjacent to a retaining wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: foam jacking a slab on grade adjacent to a retaining wall
Th mudjacksers around here are really cautious about doing garage slabs adjacent to basement walls and will take no responsibility for failure.
RE: foam jacking a slab on grade adjacent to a retaining wall
The wet weight, non-issue, even the injection pressure is likely not a problem. But if confined, then the expansion pressure could be fairly substantial.
RE: foam jacking a slab on grade adjacent to a retaining wall
"The edge of the slab on the retaining wall side has not settled..."
"The edge of the slab opposite from the retaining wall has settled..."
Both of these statements are the slab on the high side of the wall, correct?
What's the horizontal distance from the wall to the area of the settled slab?
RE: foam jacking a slab on grade adjacent to a retaining wall
However, using a foam rather than a flowable grout, it just feels that there will not be a problem.
Mike McCann, PE, SE (WA)
RE: foam jacking a slab on grade adjacent to a retaining wall
Once20036, yes the slab is on the high side of the retaining wall. It's a 10ftx10ft slab and one edge of it actually bears on top of the top edge of the retaining wall. The opposite edge of the slab is where the max settlement of 6-8 inches has occurred, but there is a constant slope from the high point at the retaining wall across the slab to the low point 10ft away. So yes, I guess its fair to assume the majority of the foam will be injected at the edge 10ft away and minimal foam will be injected directly adjacent to the top of the wall.
RE: foam jacking a slab on grade adjacent to a retaining wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: foam jacking a slab on grade adjacent to a retaining wall
I can't tell if there is a mechanical connection between the slab and the wall. There is an elevated wood deck/walkway that frames into the edge of the slab/top of the wall from the side of the wall opposite the slab on grade, but I'm not sure I trust it to brace the wall.
RE: foam jacking a slab on grade adjacent to a retaining wall
RE: foam jacking a slab on grade adjacent to a retaining wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: foam jacking a slab on grade adjacent to a retaining wall
RE: foam jacking a slab on grade adjacent to a retaining wall
RE: foam jacking a slab on grade adjacent to a retaining wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: foam jacking a slab on grade adjacent to a retaining wall