Would you take the job, walk from it, or run? 2

[JLSE]

Ive been asked to get involved with this retaining wall project (see photo), after a neighbor called the county to report the prospective client for building a retaining wall without a permit. hmm

No mention of any building adjacent to the wall, over the phone.

I dont ever want to take a "save my butt please" job anyway, especially one with construction that is impossible to truly verify to any standard equivalent to a new build..... I walked from this job.

But I would like to know, if anyone with experience has successfully dealt with a situation like this.... that is his neighbors structure, that would have been supported by his wall.

Lets assume the planned cantilevered wall was adequate to support the load. My understanding, is that it still would allow the structure above to move enough to cause some problems... differential settlement type issues.

Do you agree?

I was thinking a soil nail wall might keep the neighbors structure from shifting.... I am curious what you think.

 

[1503-44]

That doesn't look too bad, but it is also a dry day.

Maybe the bigger question is what could really be below the concrete that you can see there now.
Footing, size, number of bars??? Hard to verify now.

 

[LittleInch]

So many things wrong / not known there.

Adding the surcharge from the trench to the top surface is a no no - why did the owner of the higher property allow it? Ripe to add a collapse of that land.

What actually are the foundations of that higher house? Piled? very deep? Looks like a concrete wall in the side of the house?
Where does that drain pipe go?

What's the finished ground level? If its the original ground level then it looks better as it only about 1m/ 4ft high.

what was there before?

But it looks very amateur - a single row of starter bars in the middle onto what looks like a simple footing foundation - can't see that working....

So I would walk calmly away and watch from a distance....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XR250]

I would run very quickly away from this. No matter how well you try to cover your butt, if the neighbor gets one crack in their foundation or sheetrock, you are likely getting sued.

 

[1503-44]

He didn't allow it. He called the authorities when he saw the work being done.

There may be no footing at all, just a grade beam.

 

[Colostruct]

This really depends on several things

Most importantly is the depth of the bearing surface of the footing of the adjacent property. If the affected bearing zone is NOT supported by the wall, then there shouldn’t be an issue. In other words...the zone of influence of the supported structure should not reach “daylight” in the excavation.

To accurately determine this zone would require a soils test since this is already a contentious situation.

I’ve dealt with this situation a number of times. My usual approach is to require a geotechnical engineer to evaluate the situation and we work out a solution that includes their recommendations. That has included soil nails but for your photo I’m not sure it’s reached that level.

I’ve never walked from these sorts of projects if the owner and contractor will play by my rules. But, I do a thorough job of analysis and construction observation and a number of times, “the shoot from the hip” owner won’t want to pay for this. Then I walk.

BTW. That footing would not, likely, survive the process. It would likely need to be removed, possibly in sections, to avoid creating instability.

Drainage for this wall is also a big concern since it appears that the neighbor can discharge roof water directly behind the wall. Dealing with this might be the trickiest issue.

 

[1503-44]

Always drain a retaining wall, even in the middle of the Sahara.

 

[JLSE]

Thanks all. Exactly what my line of thought was.....
To fill in some gaps, which I took for granted: We dont do deep foundations here. This is almost certainly a 12" deep conventional, shallow, continuous perimeter footing. Im so sure of that, nothing else crossed my mind.

It is a garage, and the top of slab on grade is about where you would expect it... with maybe an 8" curb, etc.

What is missing from the discussion so far, in my mind, is the lateral confinement of the foundation. It is my interpretation, that the 7ft to daylight rule would require the bottom of the existing structures foundation to be below lower adjacent grade{edit - ie. at the top of the cantilever walls footing). (In practice, I'd be okay not going quite that far down... but sticking to academics for the sake of this discussion)... The possibility of that is so remote, its only a theoretical possibility.

And without the lateral confinement, the foundation will certainly... especially if its a floating slab (which is another certainty)... move laterally with the soil, as the top of wall deflects.

I feel confident I can deal with the surcharge. I agree, the existing foundation wont work, and would have to be removed.... a much larger toe would be required. But I can design for surcharge.

My concern, is that the unavoidable deflection of the top of cantilevered retaining wall would allow the building to move laterally, causing cracks and lawsuits.

I thought about requiring the client to indemnify and hold me harmless. Basically tell him, I can deal with the life safety aspect..... but "..you will be sued for this, and so will I, and you have to pay my costs..." But... why go through it?! I walked. This discussion is for my education..

Any thoughts and experience on the lateral confinement? Walls deflect so little.... then again, foundations dont have to move much to crack up. It sounds like those who have an opinion on a fix, think a cantilevered retaining wall is sufficient... Im interested in any thoughts.

 

[Colostruct]

This is where a geotechnical engineer is needed. I haven't heard the
"7 ft. to daylight" rule of thumb.

If I am understanding the situation now. The upper building slab is supported by the wall shown. So, the soils below the slab are restrained by the retaining wall? If I am reading the photo correctly, there might be 3 ft of retaining at the upper slab to grade? And, that footing is minimal?

Hmmm. It seems like there may be problems with the upper retaining wall already unless it is a true retaining wall or is tied back for top of wall restraint.

Your potential client may have already bought himself some liability for a poor construction problem on the neighbor's building by digging a hole next to it.

I might walk from this one...

On the theoretical note...I once did a very long retaining wall adjacent to heavily loaded slab (This was a maintenance facility for a mine building). Settlement in the slab mattered but was not crucial. I designed the wall for the active soil pressures provided by the geotech along with the wheel loads as surcharges and determined a lateral deflection at the top. The geotech and I sat down and determined that the lateral deflection of the wall contributed minimally to the settlement of the slab.

BTW, this was not an easy calc in the day. Had to dust off an old soils text book.

The soil parameters matter a bunch in this determination.

 

[Aesur]

These types of walls are done all the time when neighboring properties are at higher elevations. I would require a geotech be brought on board to provide guidance on soil friction angles, etc to determine if the existing foundation is "deep enough" to not place surcharge loading on the wall, I suspect it's not. If it's not then all the fun of underpinning the neighbors foundations starts.

The problem I always have with these kinds of retaining walls is who owns the wall. The wall is being used to support the building on the left, however is most likely on his neighbors property, so there is nothing saying he can't just remove the wall and leave. Because of this, I believe a better solution would be to supplement the existing buildings foundations with helical piles or other similar method.

As others have said, you don't know what is below the visible concrete, however I suspect that being it's cast against earth both sides, that is most likely the footing, which in this case doesn't appear to be sufficient. I would have expected to see a key and behind the wall drains installed.

 

[PEinc]

Questions & Comments:
How deep is the foundation and basement slab of the adjacent building?
Where is the property line?
Is the wall just a site retaining wall and not a building foundation wall? That is, will the wall be cantilevered or braced?
The wall footing looks to be too narrow to be for a cantilevered retaining wall.
As LittleInch said, the dowels out of the footing do not look reasonably placed or sized for a cantilevered retaining wall.
Temporary or permanent soil nails may not be an option considering how close the adjacent building's foundation wall is. In addition, a permanent underground easement may not be granted by the neighbor.

http://www.PeirceEngineering.com

 

[STrctPono]

I would run too. The craftmanship on that footing is awful and there is no way that footing is big enough. If I owned that neighbor's house, I would be pissed too!

 

[WARose]

You got me humming Kenny Rogers here.

Something already built (with no engineering) I tend to stay away from.

 

[271828]

Run. Seems likely to have a low benefit-to-risk ratio.

 

[JoelTXCive]

I don't think tie-ing the wall back is possible.

There is not enough room for a deadman; and soil nails would have to go under the home on the left. That would majorly screw up the resale value if anyone ever figured it out.

To me, the only viable solution would be a buttressed wall.

I would walk away to. This is the type thing that will run up thousands of dollars of design fees; and the customer will be ready to pay hundreds.

 

[JoelTXCive]

I just thought of this......the damage is already done. This is like getting on board to pilot the Titanic after it hit the iceberg.

There is no way the half-constructed footing will allow you to build a cantilevered wall with enough capacity; so the footing has to come out.
They are going to have jack hammer the footing; or cut all the rebar and backfill + compact.

 

[JLSE]

I think you guys pretty much nailed it. Im going to try and reply to all in this post.... I havent figured out how to link your names directly (would love a tutorial on that)
Colostruct : the seven foot to daylight was mentioned in a previous post, on this thread. Ive seen anywhere from 5ft to 10ft, in a geotech report. The code does have something.... I dont recall off-hand what it is. The structure is the neighbors, and youre right about that wall and footing. I dont know much about it. And he isnt the one who called. Its just a slab on grade garage.. with apparently some nominal retaining.

Aesur: Interesting, your solution is to address the neighbors foundation. That is a good one. I wonder if the underpinning would resist lateral movement.

PEinc : I didnt get far enough to know, but presume its a standard slab on grade with a standard garage curb height. There is no basement. The new retaining wall is a site, cantilevered wall. Not sure about the property line. I didnt even think about an underground easement.... but yeah, why would they cooperate?! What would be your solution?

JoelTXCive : I was thinking buttress wall too...

Thanks all.

 

[dik]

On a positive note... it won't likely be negative...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[PEinc]

JLSE, a possible solution is the following:
Normally, flexible sheeting walls are not supposed to hold up buildings. BUT, at this point, you could pull out the existing new footing in sections and, ideally, temporarily place some backfill against the vertical excavation to prevent any sloughing. Then, you could drill through the stabilizing fill and drill below the removed wall footing to install conservatively-designed, stiff, closely spaced, cantilevered, soldier beams (assuming the total wall height from OG to about 2' below FG in front of the wall is less than about 8 tp 10 feet). Then you could install, bay by bay between soldier beams, precast concrete lagging planks, stacking them up from the bottom of the wall up to OG behind the wall. You could install 1/8" thick plastic shims as drainage gaps between the lagging planks and also install filter fabric and clean crushed stone behind the planks. Therefore, any water that might get behind the soldier beam & lagging wall could freely drain through the wall. Keep the soldier beam & lagging wall entirely on your side of the property line.
Before starting, get am indemnity from your client for the damage that may already have been caused to the neighbor's building. And, do a pre-construction survey of the adjacent structure(s) with photos.

http://www.PeirceEngineering.com

 

[Colostruct]

At this point, the soils supporting the existing building may have already lost confinement and bearing may be compromised. At least theoretically. My gut reaction is that in this lightly loaded building and what appears to be cohesive soils that it is not an issue...yet.

I think you could construct a typical cantilevered retaining wall with special attention to increased rigidity. Backfill the wall with granular material that will not be subject to much settlement. The system should provide the restraint to the soils supporting the footings.

Of course I would have geotech look over my shoulder on all of this.

What is a bigger liability is that the existing stemwall (is it CMU?) appears to retain soils supporting the floor slab. My worry would be that this wall is not adequate and the potential movement would get blamed on the new work rather than the existing defects. Even direct shoring below the footings will not cure that issue and would cost a fortune.

I've seen this in the past on projects where over excavation compromised our upper footing support in a stepped up foundation. The geotech simply recommended concrete flow fill. It worked...so far...20 years. I'm assuming this cannot be done here since the excavation is, probably, over the property line.

I don't see an elegant method for getting out of this cleanly without cooperation from both property owners. And, I wouldn't touch it without a hold harmless from both paries.