Existing CMU Wall Repair Methods

[Romit]

Hi All,

I was working on a project where I need to come up with existing CMU wall repair method. CMU wall is inside the auditorium, supporting the seating with max. height of 11 ft. The wall is unreinforced. Major cracking can be seen in the wall face, probably due to sliding of the foundation. They don't want to tear down the wall and build a new one. I have attached few pictures for the reference. We have done the geotechnical investigation and found out soil to be sandy and very dense behind the wall. I came up with 3 different repair option.
1. Adding reinforcement #9@16" OC and embed into the footing. But I don't know how it can be done.(NEED HELP ON CONSTRUCTIBILITY).

2. Add tieback anchor. 12'-0" long Manta Ray tie back.

3. Add Micropile. 4-1/2" Dia. Casing Pile 7'-0" long at 4.5' OC

Please let me know what can be the best option and also suggest me if you have any other repair option.

Thanks.

 

[JAE]

#9 bars are not appropriate for a CMU wall in my view. And getting them into the wall and sufficiently engaged would be a problem.

 

[phamENG]

Well if they want the wall to be straight again, shoring what's above, tearing it down and building a new wall is probably the only option. Even with an anchor/pile, you'd probably end up damaging the wall further if you tried to push it/pull it back into alignment - the passive pressures would be too high.

To repair in place, there are a couple options.

Carbon Fiber Reinforcement: this involves adhering a carbon fiber or some other material to the tension face of the CMU with a compatible structural adhesive. Simpson Strong-Tie's blog has a brief primer on the subject [link seblog.strongtie.com/2015/09/strengthen-you-concrete-or-masonry-with-composites/]here[/url].​

Steel Reinforcement: This may be a little harder. Do you have access to the top of the wall to drop it in and grout it? If so, it's a bit more feasible. You'll have to break open the face shells of the first 2 or three courses. This will do two things - provide a contractor enough room to get a hammer drill in and install an adhesive dowel and then tie the dowel to the bar above (note - this isn't necessary if you're only trying to improve the flexural strength) and will also serve as your cleanout since you'll be in high lift grout territory. Drop in a continuous bar at whatever spacing is appropriate, grout with high lift procedures, and you should be ok.​

 

[phamENG]

JAE brings up a valid point with the bar size. Code allows up to #11, but clearance is going to be an issue if those are 8" blocks. However, 11 feet of un-reinforced block is likely to be 10" or 12" CMU. Even so, I would consider going to a smaller bar at 8" o/c and grouting everything given the condition of the wall. Of course that's a lot of added weight, so be sure to consider that as it relates to the existing foundation.

 

[ARKeng]

Romit: Can you clarify... is the wall retaining soil? Just trying to understand the shear/moment diagrams.

Like JAE, I'm not a fan of #9 bars especially in 8" CMU... MAYBE if you have 12"+ CMU. But if you can do #9 at 16" oc, I'd rather have #7 at 8" oc.

Several possible options I've had to employ:
1. Add external reinforcing on the tension side and shotcrete the wall.
2. Add steel strongbacks. I actually have made this work fairly reasonably with cold-formed steel sections on a basement wall, but my span was shorter and you definitely have to be concerned about stiffness and construction quality there too...

 

[phamENG]

Another key piece of information here is clearance. Looks like that's a corridor wall. How far can your fix intrude into the space and not become a hindrance to circulation?

 

[JLNJ]

If you are getting #9 @ 16, the compression force in the masonry will be too high. Something seems out of balance here.