Failure of concrete block retaining wall due to starter bar corrosion

[demayeng]

Hi,

We have recently seen a cantilevered concrete block retaining wall fail due to corrosion of the starter bars at the base of the stem where it joins the footing.

We have considered galvanized starter bars for these types of walls as a result, however predictably most builders have a problem with this.

I assume that the wall that failed had poor contact of the corefill at the base - that clean-out blocks were not used or the process was not done correctly.

Do you think doing the clean-out process is sufficient, as long as cover requirements from masonry codes are adhered to?

What are other peoples' thoughts on this?

Thanks

 

[demayeng]

It seems to me that having a hob would mean that any small amount of water that didn't fully get out the drainage holes would not be sitting against the pervious mortar joint. So even though I think it's too hard to build, i can see the benefit.

We've decided to eliminate the hob and/or galvanised bars, and just go with bitumen and polythene sheeting as waterproofing (unless a proper waterproof membrane is required).


csd72: i was exaggerating when i said the wall 'failed' - it looked dodgy so it was decided to replace it. The excavator driver said he barely touched the top of it and the whole length of wall fell over. All the starter bars along the length were apparently corroded.

 

[hokie66]

Another thing that I think makes the CMAA detail unrealistic is that the top of the footing would rarely be right at the external grade level. The drains need to exit at grade, not on the top of the footing.

 

[a2mfk]

Anything going on with the soil, drainage, etc. that may have made the water/moisture more caustic than would be anticipated? Is this near the coast? Have you been able to inspect the corroded rebar?

CMU retaining walls, especially up to 6ft or so, are extremely common here in Florida, and I have designed many without thinking about this problem. I have also never heard of this being a problem, other than maybe near the coast. Ron- have you ever seen retaining wall problems because of wall bar corrosion?

This is why I asked about the soil/site conditions, seems like a rare occurrence, but that has only been my experience.

 

[csd72]

Yes,

i am also surprised that they are all corroded. Could it be possibly due to the use of ocean sand or seawater in the grout mix. I have heard of such stupidity before.

 

[demayeng]

It was not near the coast (probably 40 kms away)

I haven't inspected it myself - I would say it is more that the core fill did not reach the footing junction properly and/or drainage was not done properly...