Frost Wall Cracks 1

[gbpackerman]

We have an attached concrete garage frost wall that has developed three cracks top to bottom about one month after pouring. the cracks widened to about 1" and top of wall dropped 3/4" over the next three weeks. Hand auger borings probes performed to about 2' below footings. Static cone penetrometer testing was performed as probes were advanced. Subgrade soils consisted of natural brown to gray/brown silty clay & exhibited very stiff to hard consistency with estimated unconfined compressive strengths of 1.5 to 4.0 tsf. Free water was not encountered. Testing did not offer conclusive causality for the cracks. Any suggestions?

 

[eric1037]

You should probably perform deeper soil borings with a drill rig. Something compressible may be deeper than your probe.

 

[gbpackerman]

Thanks Eric,
We have requested that Standard Penetration Test borings be done. Do you have a suggestion of how many borings may be needed and how widely spaced to give us an adequate and conclusive profile?

 

[CarlB]

Is there steel reinforcing in the wall? What are the dimensions of the wall? I would thing that adequate reinforcing would have prevented such large cracks.

Can you lay a long level across top of wall and note any sag or other deflection?

 

[eric1037]

I would have them go at least 20 feet deep. You probably want one in the area of settlement and at least one more in an area that hasn't settled.

You may also follow up with additional borings to delineate the poor areas depending on the results of the initial borings.

 

[dirtguy4]

Is this a heated garage or unheated? Is this settlement or maybe this is a heave issue? Does it appear to be settling close the the attached house or at the end of the garage away from the house? What is the drainage like around the garage (good positive drainage away from all buildings)? Is this garage on a pile and grade construction or spread footing and how deep are they placed? Is the garage foundation different from the house which is (basement/footing)? What is the frost depth in the area that you live, is frost getting under your foundation type and creating some problems?

 

[eric1037]

Since it's an attached garage, it's possible that the basement backfill was not performed properly.

 

[Wasdifferent]

gbpackerman,
I don't know if this is the cause of your problem, but IMHO, on any addition to a residence, the bottom of the frost wall footings should be at the same elevation as the bottom of the footings on the existing foundation. I have seen roofing material, lumber scraps, and even tree stumps buried in the backfill right next to foundations. On older homes we have even dug up automobiles that were used as makeshift septic tanks. I feel sorry for anyone who has to learn this the hard way, but that's the way I learned it too.

In residential construction, expect ANYTHING. Remember, residential contractors are legendary for their creativity in solving common problems, but very few have been awarded a Nobel Prize for their work.

-Mike

http://www.sewellconstruction.org