vertical crack on foundation retaining wall

huangyhg

vertical crack on foundation retaining wall
i have a poured concrete foundation retaining wall 32 feet long by 10 feet high (the first 4 feet are 12 inches thick and the remaining 6 feet are 8 inches thick) that has developed a vertical hairline crack from top to bottom (less than 1/16 of an inch wide). the crack does not extend to the footing. the wall is fully reinforced with rebar. since this wall retains part of a hill and is an integral part of the foundation of a house i am building i want to know if this crack is of concern? should i add a supporting column behind the crack to reinforce the wall?
any info would be appreciated.
thanks.

i would expect that you have a temperature crack in the concrete.  i doubt it is harmful other than as a new home-owner i would be upset to see cracks in the concrete walls already.  i would also expect that even though you have reinforcement in the wall it probably isn't enough.  if you are truly concerned with the integrity of the wall and are not confident yourself to check the design then hire an outside engineer to check it out for you.  this would be cheap insurance.
from the conditions you describe, it's very possible that this is a structural crack.  you should have a structural engineer check this wall for you.
few questions:
1. when concrete was placed what was the slump?
2. how did the cylinder strengths compare with the f'c?
3. is the size of the crack uniform in thickness through the height of the wall...did it go through thickness of wall..and approximately where is it located along length of wall?
4. at what age did the cracks start appearing
5. and the soil, what type is it?
6. any possibility of posting pictures here?
there are several factors that could cause the crack.  temperature, shrinkage, overloading.  is there only one crack?  as henri2 asked:  where is the crack located?  for long retaining walls, i typically detail a vertical construction joint and/or rustication joint at no more than 20 ft on center for vertical crack control.  a long wall similar to what you describe might crack somewhere along the wall due to restraining forces as the concrete cures and shrinks.  there could be more than one crack.
overloading is not likely unless the wall is tilting or moving laterally away from the soil.  hard to say without actually seeing it.
agree with aggman and jmiec, that a qualified licensed structural engineer review the wall for you.
thanks for all of your feedback.  the crack is almost exactly in the middle of the wall (at 16 feet of the 32 foot wall).  there is no expansion joint on this wall. the wall was poured about 6 weeks ago, is not leaning or moving away from the soil, and there are no other cracks. the crack is a hairline crack all the way through the thickness of the wall and top to bottom.
the structural engineer i consulted thought it was a temperature shrinkage crack.  i just wanted to get other opinions before deciding whether to reinforce it by putting another wall behind it.
thanks.
in my opinion, second guessing your structural engineer is an inappropriate use of this forum.
it sounds like a temperature crack to me.  usually the wall spans from first floor to basement floor, so a structural crack would be a horizontal crack roughly mid height of the wall.
sounds like a structural crack to me. the wall could just as easily be designed to span horizontally, and a 32'-0" long wall, 10 feet high should have had a buttress wall at mid span to resist the lateral pressure of the soil. that being said, one hairline crack is not an indication that the wall will fall down. the crack will most likely stay like it is (provided you don't park a steam roller next to the wall) and the crack can be patched with the likelihood of not opening up again. you can fur out your basement wall and hide the hairline crack forever, too.
pray like everything depends on god
work like everything depends on you.
lets assume the wall was designed to span horizontally.  
l=32'
acceptable deflection = l / 240 = 1.6 inches
:::so, the wall at midspan will deflect inwards 1.6 inches, with a crack that would probably be fairly small at midspan.  now, think of the wall in the vertical direction.  it will have deflected at midspan 1.6".  there would be a much bigger horizontal crack at midspan of the "vertical" wall, than there would be at midspan of the "horizontal" wall.  you can also think of it in the stress/strain relationship and realize that the only reason the wall is supported in the horizontal direction is because it most likely failed in the vertical direction.  the logical explanation is that it is a temperature crack due to not having control joints in 32' of wall.
cegg, i don't have a lot of experience in investigations like this, and would like to hear how this crack could be a structural crack.
i'm also curious as to where you are getting that the wall would require a buttress wall at mid span.  i've never seen a reference for this, but would love to see it.  thanks.
determining cause(s) of distress in concrete which result in cracks is a necessary step in seeking a remedial action if deemed necessary. reasons for cracking in concrete are numerous and some were pointed out by archeng59.
when performing field evaluations alongside structural engineers in the past, a document i used to refer to was aci 224. it may not be the state of the art but can help elucidate what went wrong in this type of situation.
this nrcma piece on concrete cracks in basement walls lists aci 224 as a reference.