Retaining Wall Failure and Solution 2

[Bammer25]

Hello all. A friend of a friend contractor came to me. He has a masonry house on a steep slope under construction. Anyway, he had another engineer design his below grade walls and the guy has ironically disappeared. There is significant vertical cracking of mortar joints and block near the bottom of the wall. It retains approximately 25 (yes 25!) feet of soil. 12” block filled solid with number 5 bars 16” oc horizontally and vertically.

I already told him I would not in a million years take ownership of the design and stamp it, but I’d gladly help him out for free.

Any ideas? Building a shear wall is out of the question because the basement will be finished space. Are those carbon fiber tension straps any good? I have no experience with designing them. The wall is on the order of 25’ long where it os braced by other walls turning 90 degrees. He has all gravel (no soil) backfill and plans to pour a driveway (so more loading from cars).

I don’t want to tell him to kick rocks but this doesn’t look good to me. I’ll upload a picture in another post looking from the road.

 

[Bammer25]

Picture before backfilling

 

[dik]

First, he has to get in contact with a good geotekkie. Problem could be serious enough that the foundation wall needs replacing or major reinforcing.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

#5 at 16" feels very light for a wall of that size. Did the cracks happen before or after the floor was built? If after, what is the condition of the floor diaphragm to wall connection? Was it designed as free standing? (I doubt it.) Was shoring used during construction?

Edit: you posted a picture

 

[phamENG]

Have any pictures of the cracks?

 

[JoelTXCive]

How many feet of wall have been constructed. If it's just the sections in the above photo; then I think it would be easiest to demolish and start from scratch.

 

[JoelTXCive]

Maybe you could install horizontal whalers and then soil nails going out into the backfill?

 

[Bammer25]

The whaler (maybe a c channel with tie backs through the wall and encased in concrete was my first idea.

No cracks formed before he backfilled with gravel. The walls were fine after construction and grouting for weeks.

Correction the horizontal bars are 16” and the verticals are every cell

 

[XR250]

I think you would need tiebacks regardless. I can't imagine the floor diaphragm taking the kind of force.

 

[MotorCity]

Can you add another wythe and tie it to the existing wall to arrive at a wall that is 24" thick? There's no way a 12" wall works, even it was solid concrete if it retains 25' of soil. What does the foundation look like to prevent overturning?

 

[phamENG]

I'm curious why it's cracking with no lateral load applied.

XR - maybe it's going to be a concrete slab?

 

[Rabbit12]

Who designed this in the first place? You say he disappeared? I assume he's licensed and if so this probably warrants a call to the board if this is in the US.

I'm just in the middle of a project with 20'+ CMU walls and we have #6@24" for just wind/seismic with no backfill. I'm with Pham seems light to me. Certainly there was some diaphragm bracing that was considered during design.

 

[Bammer25]

The
Wall is completely backfilled with gravel. There is a ton of pressure on it. It’s the front of the house (cabin style) with a walk out basement in the back. The front wall serves as a retaining wall and will support the driveway pressure as well.

I just found out the engineer that stamped this is deathly ill with some sort of brain condition I am not sure on the foundation but it’s probably under designed.

I’m going to go look at it with him next week.

 

[BridgeSmith]

If the anchorage of the return/perpendicular portions of the wall are adequate, it could work, since those sections would act as shear walls. It would be a complex analysis to undertake, though.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[phamENG]

Ah. Yeah. That's a bummer. Remove and rebuild is likely the best scenario. Remember, if it's finished space, waterproofing will be critical. Is there waterproofing installed on the outside face? Can it withstand the movement? If it's a paint on kind it probably can't. You may be able to reinforce for strength, but there are a lot of other issues that could come of this that are only tangentially related to the strength of the structure.

 

[PEinc]

Besides tearing down the wall and rebuilding with a properly designed wall, could you excavate behind the wall to a safe stable slope and then backfill with styrofoam blocks? There would then be no pressure on the wall and you could build your driveway above the styrofoam.

http://www.PeirceEngineering.com

 

[ATSE]

Agree with PEInc.
Geofoam is your friend. You may need a multi-pronged approach. Don't simply think of adding strength. Reduce load.
Increase strength and reduce load and ensure slope stability.
With my 38 second perspective, I'd say slope stability and long term creep is the top of the list for concerns.

 

[SteelPE]

Hard to tell about the extent of the damage from the photo you gave. What about slope stabilization similar to the way they stabilize the earth using a Mechanically Stabilized Earth Wall (MSE Wall). They use geosynthetic fabric to eliminate a good portion of the soil pressures on the backside of the wall.

I have never designed a wall this way, and I have no idea how you would go about doing it...... maybe contact your local MSE supplier to see if they can assist.

On the other end. I designed a wall a year or so ago that was retaining on the order of 17' of backfill (for a building which was higher than the grade was). The wall ended up being 24" thick poured in place concrete with #8 bars at 8" o.c. on the inside face and #5's @12" o.c. on the outside face. I was worried that when they backfilled the wall the wall would lean out causing AB issues with column we had placed on top of this wall. The GC came back later and said the wall moved fractionally during the backfill process and was nothing to be worried about (the steel fit so it didn't move much at all).

So, I don't think your wall would work at all.

 

[Bammer25]

Not familiar with geofoam. Good ideas guys. I am sure he does not want to rip it down and start over but he strikes me as a safety first guy, not a profit first guy

 

[Aesur]

I suggest starting with obtaining a copy of the plans/engineering from the contractor. Right now it seems like there are a lot of questions about how this was designed.