Not repairing bulging basement walls

[jay156]

I have a house I recently inspected with bulging basement walls. They are CMU, 10 courses high and bulge approximately 1" at mid-height. According to the realtor, water seepage hasn't been a problem, and I didn't see any staining.

I know there are many remedies for this, and I can search other threads where that has already been discussed, but what the client wants to know is, do they represent a danger of collapse if they are not repaired? The house is about 30 years old, so the walls have been in this state for quite a long time now.

What I'm thinking of advising is to keep an eye on them and if they bulge any more or develop any additional cracks, they should be repaired immediately. Is that good advice?

Thanks.

 

[J2CUB612]

It seems your question is impossible to answer without a lot more information. 1" of deflection in what must be about an 8 ft wall is a big number.

The question is answered with engineering methods though.

What is the reinforcing? What strength does the wall have including Pdelta from the deflection? Is there reserve strength? What is the loading? Any drainage problem that would cause hydrostatic loads? Is the wall connection adequate especially at the top?

If all of these questions can be answered then you can probably make a decision about what to tell the client.

 

[ATSE]

In practical terms, homeowners like to spend their money on kitchen countertops and new carpet, not on foundations and basement walls, so you may want to use strong language in your report, lest your recommendations get put on a shelf.

The wall is creeping and will probably continue to creep. The lateral loads may be increasing due to overburden or wetting. J2C is right to bring up p-delta. Famous last words, "It's been fine and hasn't fallen down for 30 years..."

One idea for mitigation is to leave the wall alone and reduce the lateral load by removing backfill soil and pouring controlled density fill ("2-sack slurry") in the 2'-0" zone behind the wall, say 1/2 up the wall height. This will drop your lateral loads down significantly because you've disrupted the inclined failure plane.

You probably won't make friends with the homeowner, and the homeowner will say it's too expensive and cumbersome, but you've done your job.

 

[dcarr82775]

I don't think the low density fill reduces the loading on the wall at all. It would lower the stresses because there is a thicker section (fill + wall) working to resist it, but the loading remains the same.

 

[msquared48]

Since it is retaining earth, the wall should be reinforced and have FULLY grouted cells below the ground level. You need to check and make sure that is the case.

Ask these questions to yourself: Is the wall cracked on the inside? Could the wall have been constructed this way? Could the wall have been backfilled too soon when initially constructed?

Do not totally rely on the seller or the realtor that this is an old problem. They have a financial intersest in the problem that is not to your advantage.

I agree thaqt some repair recommendation needs to be made to CYA. The call you will and should make is whether or not the wall is an immediate safety hazard.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[ATSE]

dcarr,
This may be getting a little off topic, but I would respectfully disagree regarding replacing soil with a cemented block and lateral loading.

The larger the cemented block (CDF or cemented soil) behind the wall, the lower the effective lateral load the wall feels. For a very large cemented block, there is no lateral load on the wall. Similar mechanics (albeit different) to an MSE wall, where the Keystone blocks have no flexural capacity, and the mass behind the wall (held together by geogrid, but could be cemented soil as well) is the resistance.
The main differences are strain compatibility and the aspect ratio of the cemented block. I agree that a tall slender block would do little, but if the block is at least 1/2 wide as it is tall, you have changed the sliding failure plane's affect on the wall.

 

[BAretired]

Ten courses of block would be about 80" high, 6'-8". I have inspected numerous brick foundation walls 80, 90 or 100 years old. They are usually about the same height as yours and unreinforced.

While it is possible that these walls could last another 20 or 30 years without repair, in my experience the bank providing mortgage funding will demand a report from an engineer stating that the walls are sound. Most engineers, including me, are not prepared to do this, so remedial measures are the norm.

Most of these walls were repaired using 2 x 6 PWF studs inside the masonry, fastened to a bottom plate anchored to the concrete floor and a top plate anchored to the wood floor above.

BA

 

[ToadJones]

If there are visible cracks in the inside then the parge and tar coat on the outside is toast.
If this is the case, water problems are almost a certainty in the future.
I have actually seen some masons construct walls that poorly in the past but you would be able to see in the masonry work if they were off through the middle courses and then brought back towards the top..as MMC suggested. If built poorly, there maybe no cracks.

 

[dcarr82775]

ATSE,

I think our difference is semantics. The lateral earth pressure is the same with or without fill. For a 2' thick chunk on an 8' wall I think the earth pressures are the same, but now there is the added weight of fill that would help counteract the driving earth pressures so the stresses are lower in the original wall, but the loading hasn't changed. With large thickness of fill the original wall sees less and less stress, but the loading never really changes

The fill would need to be placed in small lifts or it would easily exert more pressure on the existing wall than the soil.

 

[concretemasonry]

Depending on the thickness of the wall, 10 courses is really not a "tall slender wall".

In our area, we have 10's, if not 100's of thousands of 12" unreinforced CMU basement walls that are performing well and were built according to the code standards. Most are actually 12 courses, but many newer ones are 13 courses (over 8'clear height, which precipitated some reinforcement. There are more problems and higher costs with 8" reinforced concrete walls in residential construction.

I know of several engineers that became confused and and gray (if not bald) trying to make engineering calculations on a wall by looking at is a tiny 1' wide vertical strip and trying understand why they do so well through the years. Usually the "simplifying" assumptions made for calculating ease/time are the problem. Neglecting the effect of corners and using falsely assumed block and mortar strengths drastically affects the calculations and make them unrealistic. Obviously, the end walls that are unloaded vertically are the biggest problem areas. I have played with this problem/enigma for many years and almost got run out of an ACI 530 code writing meeting (see the ACI 530-02 list of MSJC members of the group that wrote the code) for suggesting something that was intuitive, proven, but beyond putting into a code since it was beyond the respected the ability of typical structural engineer.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[DWHA]

dcarr

I think that if you were to pour your 2' think chuck of concrete you could begin change the direction of the span (especially if you are pouring it in lifts). Rather than the wall spanning from footing to main level floor, it could begin to span from corner to corner of the structure. And these corners are strong, therefore your solution very well could help. The load does not change, however the load path will.

 

[joshmaughan]

You need to x-ray the wall and determine how it is reinforced. If it is not reinforced................game over........walk away. There will be problems down the road. If is is reinforced, and analysis determines the secton has capacity to resist the loads and added 1" eccentricy, you should be okay. Then excavate and coat the entire outside with XYPEX or other waterproofing system. All of this is expensive, but should work. X-ray around $2000. XYPEX about $0.75 per square foot of wall. Exavation $???.

 

[csd72]

I disagree with a large number of the comments above.

1 in 96 deflection is not a ridiculous amount and I would suspect that the wall would probably be stable as long as that did not increase.

I have seen brick houses with much lager deflections that were still stable.

That said, I would NEVER make a recommendation for a building defect without determining the root cause. Anything else is bound to end up just treating the symptoms.

Is it frost, moisture, tree roots or just poor soil? If the cause was treated, would these prevent any further movement?

 

[bridgebuster]

Pachometer is a lot cheaper - and very effective - and a lot safer than an x-ray.

Can you post a photo?

I've inspected a lot of stone retaining walls - cut stone and dry rubble - most have a bulge or displacement, still standing, some are on the order of 30+ feet tall, and most of them are quite old.

I like BA's solution.

 

[racookpe1978]

Bump for reference.

 

[smb4050]

An interesting post and why I visit this site. This is a common (maybe even simple) problem that isn't all that simple to resolve. To me an engineer will never have all the information needed to determine an engineered solution because of the cost to do additional testing. I could never recommend a $5,000 plus engineering expense (x-raying, excavation, etc.) to a homeowner for a 1" bow in a masonry wall. To me that is borderline ridiculous. J2CUB612 had a really good response with the questions asked, and BA nailed the correct solution to recommend.

Concretemasonry please expand on your previous post. I think I agree with it, but got confused at the end.

We'll never know the various loads on the wall or the walls structural response to the loads due to cost constrains getting all needed information. Like concretemasonary, I spent (too much) time studying it, so now my response is “I don't do residential inspections”.