CMU wall tie back

[ztengguy]

Earlier this week I posted about a Bowing CMU wall. The building department is adamant about some remidiation to be done, so we are going to look at tie backs at the slab. The wall goes down to the footing, forming a retaining wall of about 4 feet above grade. I am proposing to cut back the slab, excavate down and insulate and new backfill (one official said that the bad soil was putting 20TSF pressure on the wall), and then a new fill in slab with tie backs.

Anyone ever done this, and have a detail? I was thinking hooked bars into the cell, and then grout solid down to the bottom of the wall. The owner wants to try and pull the wall back first, before doing the backfill slab. I might be inclined to try that, perhaps some bracing anchored through the wall and slowly draw the wall inwards?

What have you done before?

Thanks

 

[hawkaz]

20 TSF??? I could believe up to 65 psf. No anchorage is going to resist 20 TSF of retaining.

I would have expected the wall to have been solid grouted below grade. Have you opened it up to confirm what is in place?

Dowels to the slab are fine, but how far back will you need to go. Frictional resistance of a slab alone won't help much unless you go pretty far in.

You can try pulling the wall plumb, but unless you permanently brace it or strongback it, I suspect the wall will just return to it's current position once it is released.

 

[msquared48]

I also agree that the lateral loading must be a typo. Perhaps 40 psf/ft with a surcharge loading, but not what the BO said. You really need to make some points here and ask him what he has been smoking!

To resist the load, the wall would have to have been grouted full not only below the slab, but at the vertical steel cells too. You can tell the spacing of any grouted cells by the pitch when struck with a hammer.

Sounds like the wall is retaining earth inside the building on which the slab sets. Doweling into the slab will help stabalize the top of the wall, but will not relieve the bowing. The wall would have to be deloaded, put back into the proiper positioning, properly reinforced and grouted for the load it will see, and then properly backfilled with small equipment with a free draining material. Not a small undertaking.

On thinking about this, it is possible that when the backfill was originally placed, the soil was overtampoed or saw too much surcharge load from compaction equipment, causing it to bow. Seen that happen before many times, unfortunately.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

Could you provide a sketch of the current situation?

BA

 

[ztengguy]

Here is a sketch. im 99% sure its unreinforced, so not good as currently shown.

Yea, I know 20TSF is alot, but who wants to argue with the building official. This is a bit political too, 3 gents from the Building dept came out to voice their opinions, sorta felt ganged up on. Also the owner isnt exactly helping, he has done some work, then tried to get it approved. blah blah.

A bit of me wants to walk away. Might not be ethical though, but gut feeling says too.

 

[BAretired]

It is a nasty problem. If you are unsure about what to do, there is nothing unethical about walking away.

BA

 

[msquared48]

Kinda what I thought the situation was. If the BO is unreasonable though, I would walk away. The forces are totally unreasonable for the situation.

If you want to pursue this further though, you sould ask to see their calculations that generated the lateral forces and see what happens.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com