V-shaped Cracks in Concrete Foundation Wall

[garpike]

I came across some unusual cracks today while inspecting the unreinforced concrete foundation of a semi-detached two-story home in Eastern Ontario. The side exterior wall (on the detached side) has 4 diagonal cracks in two roughly symmetrical V-shaped patterns which begin at each end of the wall (see photos below). There is also a vertical crack running down from the other side of the window. The wall supports two steel beams which appear to support both the first and second floor joists. Roof trusses run parallel to the wall supported on the front and back walls. The cracks have been "repaired" but most of them have reopened. All other basement walls appear to be free of cracks (although they are not all exposed).

I thought it might have been cold-joints from poor construction, but it seems unusually that there would be two of them that are roughly symmetrical.
Could some strange settlement be the cause?
Shrinkage?
Vibration? (there is a regularly used rail line about 40 m away)
Could it be earthquake damage?

Any idea what could cause this?

 

[jayrod12]

Do you have any information on the foundation type below? Pads or piles?

It could be the steel beam is providing horizontal restraint, as is the slab at the bottom of the wall. Therefore the backfill pressure it causing these kinds of crack patterns.

 

[msquared48]

It would have been nice to know if the cracks were uniform or varied in width before the patch and sack was done.

Uniform implies what jayrod mentioned regarding the steel beam restraint

Wider at the top than bottom would imply a hard point beneath the V in the foundation restricting vertical settlement, as in a large boulder or pile.

If the cracks were apparent inside, but not outside, then excess backfill consolidation is suspect.

Combinations of the above are possible too...

The cracks tell all... usually.

Mike McCann, PE, SE (WA)

 

[dik]

almost looks like a concrete placement issue, except for the crack from the window corner... but even that might be related to the forming of the window...

Dik

 

[garpike]

The wall bears on 8" thick by 20"~24" wide strip footing. Probably on clay.

The steel beams are probably providing lateral restraint, but strangely one of the beams is approximately centered over the V-shaped crack, while the the other beam is directly over where the other crack starts.

The cracks in the grout do appear to be slightly wider higher up on the wall. The worst being about 2 mm near the the top and 0.5-1 mm near the bottom. It is also interesting that the cracks appear to stop just above the floor slab (although it is hard to tell with the repair).

The idea of a hard point restricting vertical settlement might make sense, except for the symmetry of the two V-shaped cracks. The bottom of the V of each is about 20 feet apart, and each V starts at the end of the wall on each side. I guess there could be two boulders with their midpoint coincidentally centered on the foundation wall.

I could not see any cracks outside due to 2'-3' of snow. The owner said there are some fine cracks in the parging that may or may not line up with those inside.

 

[MotorCity]

Agree w/ dik, looks like a placement issue. Perhaps a cold joint that was "patched" from the inside. The V-shape looks like it could be formed by the natural flow of concrete throughout the formwork. Almost like it was poured from two different sides and they ran out of concrete, came back and filled in the "V". If this is residential, they probably did not vibrate the concrete as it was placed, so it just flowed by gravity through the forms....hence, the sloping effect.

 

[jayrod12]

If it was a concrete pouring issue, I wouldn't expect the V to extend all the way to the base of the wall as shown. I've seen diagonal pour joints, but they always terminate around the bottom 1/3 point of the form. The vertical weight of the concrete will fill at least a portion of the formwork. Further, I've never seen a residential pour with concrete so thick that it would hold that steep of an angle of repose. If anything, residential concrete is normally soupy as post hot wings excrement because they don't want to vibrate it.