Frost heave at interior spread footing
Frost heave at interior spread footing
(OP)
I am having an addition built and the spread footing for a 28 foot long central girder has heaved. There are three concrete filled columns approx. 7 feet apart, and all of them have forced the girder to rise, one by about 1.5 inches. What should the builder do to correct the problem, cut the columns down, excavate the footing and pour a new one? The winter has been extremely long and cold, and the exterior wall foundation shows no signs of heaving. The footing depth is about 7' below grade but the interior footings were subject to freezing because the house is not insulated or heated yet. Any thoughts would be appreciated. ASCII





RE: Frost heave at interior spread footing
Recommend you request the contractor hire a structural engineer to evaluate and approve a repair or have the contractor remove and replace the faulty components.
RE: Frost heave at interior spread footing
RE: Frost heave at interior spread footing
CarlB's suggestion is also one to consider except it has been my experience that once soil has been disurbed it like worms in a can will not fir back into the same volume.
RE: Frost heave at interior spread footing
I'm not sure what you mean by concrete filled columns. If you have concrete posts supporting your floor beam then I'd say it's an unusual structure. I'm guessing what you meant to say was "buried concrete piers, with a post of some kind on top of the pier". And the post supports the floor beam. Yes?
RE: Frost heave at interior spread footing
If your problem is frost heave then there are 3things which must be present - a frost susceptible soil, water and freezing temperatures. According to the theory, the absence of one of these would prevent frost heaving from occuring. The depth of founding of the footing (2m approx) in some areas is sufficient by rule of thumb. However, this might not be the case in your situation. Presumably you had an investigation done to determine athe subsoil conditions. Too often this is not done and past experience is used.
Patios or walkout extensions to homes that are not to be heated are often founded on piles to go deeper than the depth of frost penetration. In your situation it might not have beeen a problem if the extension was done in the summer and the heat was on for the next winter etc. What happens, however,if your heat is off a winter for some reason after the building is in service. Then the situation you are experiencing is likely to occur. It is good that the situation is caught now than after the extension is completed and in service.
Regarding fixing the problem. There are a few possibilities. However, you may have to await the warm weather when the heaving has subsided. If this is impractical based on work to be done then some heat will have to be used to keep the footing areas warm as Carlb has suggested and allow the heave to subside. Other solutions are the use of insulation over the area encompassing the footings, or screwpiles to retrofit existing foundation. Both of these are best done in the spring/summer after heave has subsided. There are probably some other solutions depending on site conditions.
It would be a good idea to monitor the heave/subsidence. Curious why the exterior footing shows no sign of heaving
Good luck
RE: Frost heave at interior spread footing
ASCII
RE: Frost heave at interior spread footing
If a 1/2" bar can be pounded down in the vicinity of the footing without encountering a void (possible to miss it) then it can likely be constructed on the same footprint. Local geotekkies have a bar and heavy pipe with handles and an endcap to drive the rod (seems to work OK in clays). Because of the extreme movement of the foundation that I did the report on, my recommendation was to use a different location (some other place on site that had adequate frost cover) or to found the new footings on soil below the depth of penetration (and hope there wasn't a more pervious seam to keep from pumping the lake)
CarlB:
My earlier querie regarding supercooled water in clays was in reference to this project.
RE: Frost heave at interior spread footing