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CMU Retaining Wall leaning forward

CMU Retaining Wall leaning forward

CMU Retaining Wall leaning forward

(OP)
I'm investigating a wall that is approximately 300' long and 10' high. the wall is leaning out away from the retaining side by 1/2" - 2 1/4" inches. The contractor is claiming that 2" out of plumb in 10' vertical is an acceptable industry standard (this is in New Mexico, bear with me) my position is that there is no allowable tolerance for being out of plumb. I'm having a hard tme finding anything published that states one way or the other. Beyond common sense, does anyone know of a resource to answer this?

RE: CMU Retaining Wall leaning forward

I don't know of any such tolerance.  I assume as you are talking to the contractor who built it that this is a relatively new wall, and if that is the case, he is just trying to avoid responsibility.

My guess is that either the footing is too small or the reinforcement is not in the right place.  Either way, the leaning will probably get worse.

RE: CMU Retaining Wall leaning forward

1" of rotation is normal, necessary and planned for by battering the face.  2" is probaly OK if no further movement occurs, (unlikely).

RE: CMU Retaining Wall leaning forward

cvg's reference would give about 1/4" tolerance, but I think that is for built out of plumb, not rotation.

civilperson is correct in that the face should have been battered, but it is seldom done with CMU walls.  If this movement has occurred in a short period of time, it is beyond normal.

RE: CMU Retaining Wall leaning forward

sounds like the contractor is still on the hook for this so either it was built out of plumb or started leaning shortly after it was constructed.  For the second case, it may have been designed incorrectly. Either way, I think the tolerances would still apply during the contractors warranty period.

RE: CMU Retaining Wall leaning forward

Designed incorrectly or built incorrectly.  If the contractor built it to a poor design which wasn't of his doing, he is not responsible.  If he built it poorly, he is.

RE: CMU Retaining Wall leaning forward

i'm fairly certain that aci and/or ibc (not sure which one) mention construction tolerances. i suppose the trick would be figuring out if it was built out of whack and hasn't moved at all OR if it was built perfect and is now moving OR was built a little out of whack and is moving. i suggest you take measurements (from top to near bottom) with a plumbbob at intervals along the wall and record the data. come back at some time later at the same locations and see if it moves. if you know how old the wall is then you might be able to ballpark when the readings will provide indication that the thing is still moving (if it is indeed moving). you might also revisit the paper trail of inspection reports (footing, rebar, drainage materials, backfill materials, etc), foundation reports, design dimensions, etc.

realistically (for construction tolerances...not movement) from my perspective, a "good" wall is within a 1/2" or less and an "kinda sorta okay" wall is 1" or less for a 10' height. however, i have seen fairly strict construction tolerances from the EOR for CIP retaining walls.

and never take a contractor's word for anything...whether you actually know the answer or not...

RE: CMU Retaining Wall leaning forward

Just for what it's worth I recently investigated a similar situation and found the reinforcing in the wrong face of the wall.

RE: CMU Retaining Wall leaning forward

hokie66 - we also investigated the same situation with the rebar in the compression face not the tension face for a bulging concrete retaining wall. Other construction oddities included foundation steel only tied into the wall every 7 feet.  However, it was built 95 years ago and still standing.  We will probably leave in place and buttress it...

RE: CMU Retaining Wall leaning forward

cvg, yes, there are a lot of walls which serve perfectly well in spite of poor construction.  Some unreinforced brick walls actually do well for a long time, but then start to lean.  Sometimes there is no justice.

RE: CMU Retaining Wall leaning forward

(OP)
Thanks everybody for responding so quick, I found that several states publish their construction specs for public works online. The consensus seems to be 1/2" - 3/4" out of plumb in 10' vertical is acceptable. cvg and hokie66 are both correct, we did find that the reinforcing was on the wrong side of the wall.

 

RE: CMU Retaining Wall leaning forward

In which case, the wall will eventually fall over.  There are only two options:  pull the wall down and start over, or drill through the wall in the top part and install tiebacks.  Well, there are other options, but these two would probably be the ones you want to consider.

RE: CMU Retaining Wall leaning forward

Has anyone checked the type of backfill that was used behind the wall,and the method that it was placed?? The moisture content of the material could create "bulking" of the soil if it is placed "dry" and then gets saturated.

RE: CMU Retaining Wall leaning forward

Is it leaning or did the wall rotate? Most out of plumb issues have nothing to do with the masonry but the footing settling, compaction issues... At least thats what our issues have been :)

RE: CMU Retaining Wall leaning forward

I see that you already found a very likely cause of the problem, and I think we can all learn from this scenario- specify the tolerance in the specs. In this case you could easily refer to the specs which the Contractor would have to adhear to.  Personally, if I see a wall CMU wall rotated 2 1/4" inches in 10ft, I would be very concerned.  I notice one case with a MSE wall that the wall started tipping forward after the contractor was operating a crane close to the edge of the wall.

RE: CMU Retaining Wall leaning forward

C'mon guys - back to basics:

It doesn't matter in which face the wall is reinforced, that could not explain a lean in the wall, maybe cracking, but not a lean.  The wall is rotating, apparently about the toe, so it is a global failure rather than (or additionally to)a structural one.  My first guess would be that the fill used behind the wall is significantly weaker, or more poorly drained, than assumed in the design. My second guess would be that the foundation soils are weaker than assumed and aren't strong enough to support the toe pressures.  

RE: CMU Retaining Wall leaning forward

MSEMan,

This question has been asked and answered.

Back to basics indeed.  If the reinforcement is in the wrong face, as the OP has found is the case, the wall certainly will lean.

RE: CMU Retaining Wall leaning forward

MSEMan, It is very possible for a CMU wall to lean forward on good soil.  From a structural perpective, this type of wall may be considered flexible at the connection to the base, and with the reinforcement on the wrong face of the wall, the wall would even be more susceptible to that type of defect.

RE: CMU Retaining Wall leaning forward

"this type of wall may be considered flexible at the connection to the base"

I find it difficult to design with this assumption.
I always assume a cantilevered wall has a fixed connection to the base.

I know the question has been dealt with, but I wouldn't be suprised at 0.5" movement at the top of a 10' wall.  

RE: CMU Retaining Wall leaning forward

A 0.5in is not much I agree. However, 2.5" should be looked at more in details.  It would be nice if we can
have the wall's dimensions.  

There could be several reasons for these deflections one of which is construction procedures.  Did the contractor perform any compaction behind the wall ?

If not, I am willing to bet that the 2.5" is occurring towards the middle of the panel and the 0.5" towards the edges.  If that is the case, the design should be looked at again.  It does not necessarily mean that the wall is going to fall (we're reinforcing a 100' long wall that bulged and tilted in excess of 4" and it has been holding for the past 2 years), but it should checked again to make sure that it is inded performing as it should.

RE: CMU Retaining Wall leaning forward

bridgebuster, thanks for the pic.

If you model such a wall and assume say a thickness of 8-9"  the expected deflection with a fill with a friction angle of 30 degrees, the expected deflection is in the order of 4-5" assuming no hydrostatic pressures.

RE: CMU Retaining Wall leaning forward

Doc,

The wall didn't have any weepholes. The upper side of the wall supports a service road that sees quite a bit of bus traffic. At the time of our first inspection in 2005, the asphalt pavement and drainage was in poor condition. A month after our first inspection we went back to check and discovered that some sections had moved up to 2".

The is a water main and sewer underneath the service road. Our assumtion was that one or both were leaking and building up the hydrostatic pressure along with the poor surface drainage.

Our client decided not to investigate and just braced the wall. It's presently under construction.

 

RE: CMU Retaining Wall leaning forward

apsix,
Are you saying that you believe there is a rigid connection between the base (which is normally a thick reinforced concrete section) of the retaining wall and the vertical CMU portion? You are implying that the base slab will rotate at the same rate as the CMU portion? For a thick reinfoced wall, I could imagine that, but not CMU.

RE: CMU Retaining Wall leaning forward

The basis of the design of a cantilever wall is a rigid wall to base joint.
A CMU wall is slightly less stiff than a CIP wall of the same thickness, but not enough to class it as having a flexible conection to the base.

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